Call

Astrophysical and Local Tests of the Einstein Equivalence Principle

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

The Einstein Equivalence Principle (EEP, which Einstein formulated in 1907) is the cornerstone of General Relativity (only formulated in 1915) but also of a broader class known as metric theories of gravity. Although they are often confused, the two are conceptually distinct, and different experiments optimally constrain one or the other. Recent developments, including quantum interferometric tests and dedicated space missions, promise to revolutionize the field of local tests of the EEP and dramatically improve their current sensitivity. This thesis will explore new synergies between these imminent new local tests of the EEP and ongoing or planned astrophysical and cosmological tests: some of these directly test the EEP, while others only test GR on various scales. We will explore relevant paradigms (including scenarios with and without screening mechanisms), develop a taxonomy for various model classes, and study how they are further constrained by experiments such as MICROSCOPE and ACES, in combination with astrophysical data from ESPRESSO, ALMA and other facilities. The work will also be directly relevant for the science case of several ELT instruments, as well as Euclid and the SKA.

New Maps of the Dark Side: Euclid and beyond

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

The growing amount of observational evidence for the recent acceleration of the universe unambiguously demonstrates that canonical theories of cosmology and particle physics are incomplete—if not incorrect—and that new physics is out there, waiting to be discovered. The most fundamental task for the next generation of astrophysical facilities is therefore to search for, identify and ultimately characterise this new physics. The acceleration is seemingly due to a dark component whose low-redshift gravitational behaviour is very similar to that of a cosmological constant. However, currently available data provides very little information about the high-redshift behaviour of this dark sector or its interactions with the rest of the degrees of freedom in the model. It is becoming increasing clear that tackling the dark energy enigma will entail significantly extending the redshift range where its behaviour can be accurately mapped. A new generation of ESA and ESO facilities, such as Euclid, the ELT, and the SKA have dark energy characterization as a key science driver, and in addition to significantly increasing the range and sensitivity of current observational probes will allow for entirely new tests. The goal of this thesis will be to carry out a systematic exploration of the landscape of physically viable dark energy paradigms and provide optimal discriminating observational tests. The work will initially focus on Euclid (whose launch is fast approaching) and will gradually broaden to explore synergies and probe combination with the SKA and relevant ELT-HIRES instruments.

High-performance timing detector for the HL-LHC Upgrade of the CMS experiment at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 144 - Joao Varela

Co-Supervisor: 1704 - Tahereh Niknejad

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

In the High-Luminosity phase of the LHC physics program, the accelerator will provide an additional integrated luminosity of 3000 fb-1. One of the main challenges that must be overcome is the very high pileup (PU) originated by the high luminosity. Each of the colliding beams at the LHC consists of many intense bunches of protons. At the HL-LHC, the average number of interactions in a single bunch crossing is 200 (named ‘pileup interactions’). Most of these interactions are not interesting in the searches for New Physics at the TeV scale. They contain low transverse momentum (pT) particles and deposit little energy in the CMS detector. A relatively small fraction of all interactions are hard collisions producing particles with high pT. Nevertheless, the presence of tracks and energy from 200 extra collisions degrades the reconstruction of the hard scatter. Pileup produces many hits in the tracking detectors, leading to mismeasured or misidentified tracks. It also adds extra energy to the calorimeter measurements, such as jet energies, associated with the hard scatter collision. Electroweak phenomena, which are of special interest, are often characterized by having isolated leptons. Energy or tracks from pileup can contribute to an activity that is not due to the collision containing the leptons or photons and cause them to appear as non-isolated. In general, pileup confuses the reconstruction and interpretation of events. The development of a new Timing Detector to be integrated in the CMS experiment aims at fighting the pileup background, substantially improving the sensitivity to New Physics. In the time domain, pileup collisions at the HL-LHC will occur with an r.m.s spread of approximately 180 ps within the bunch crossing structure of the colliding beams. Slicing the beam spot in consecutive time exposures of 30 ps allows to reduce the number of vertices per exposure to about 30. A time resolution of this order would, therefore, reduce the effective multiplicity of concurrent collisions to a level comparable to the present LHC. However, the required time resolution is one order of magnitude better than achieved in the current CMS detector. The Timing Detector (MTD) is a dedicated timing layer in front of the calorimeters capable to measure the time of charged particles with a precision of 30 ps. The subject of the PhD thesis is the development of a new timing technology based on state-of-art LYSO scintillating crystals, associated to silicon-photomultipliers and Application Specific Integrated Circuits (ASICs) developed at LIP in collaboration with Portuguese industry. The thesis work will be done in the context of a collaboration with several institutes in Europe and in the US. The LIP-CMS group is fully responsible for the design and construction of the readout system of the 330’000 sensors composing the Barrel Timing Layer, benefiting from a long experience in the development and leadership of large instrumentation projects. The development and test of prototypes is carried in the TagusLIP laboratory at Taguspark, Oeiras. Stays at CERN to perform tests and measurements with dedicated proton beams at the SPS will be required. Visits to other research facilities to perform tests of resistance to radiation of the prototypes detectors and electronics are also foreseen. The research will be carried in the frame of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”.

Fundamental cosmology from precision spectroscopy: from ESPRESSO to the ELT

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

ESPRESSO is the next generation spectrograph, combining the efficiency of a modern Echelle spectrograph with extreme radial velocity and spectroscopic precision, and including improved stability thanks to a vacuum vessel and wavelength calibration done with a Laser Frequency Comb. It is installed in the Combined Coudé Laboratory of the VLT and linked to the four Unit Telescopes (UT) through optical Coudé trains, allowing operations either with a single UT or with up to four UTs for about a 1.5 magnitude gain. One of the key science drivers of ESPRESSO is to perform improved tests of the stability of nature’s fundamental couplings, and in particular to confirm or rule out the recent indications of dipole-like variations of the fine-structure constant, alpha. In this thesis the student will be directly involved in the analysis and scientific exploration of the ESPRESSO fundamental physics GTO, and in the preparation of any follow-up observations. Apart from its obvious direct – and very significant – impact on cosmology and fundamental physics, the ESPRESSO data will also be important as the first reliable precursor of analogous high-resolution spectrographs for the next generation of Extremely Large Telescopes, and in particular of ELT-HIRES (in whose Phase B we are directly involved). A second goal of the thesis is to use the ESPRESSO data for detailed realistic simulations to assess the cosmology and fundamental physics impact of ELT-HIRES, also including tests beyond the sensitivity of ESPRESSO, such as redshift drift measurements and molecular tests of composition-dependent forces.

Effect of strong magnetic fields in the inner crust of neutron stars

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1709 - Helena Pais

Co-Supervisor: 1710 - Francesca Gulminelli

Co-Supervisor: 174 - Constança Providência

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: Mixed

Abroad-Institution: LPC (CNRS/ENSICAEN/Université de Caen Normandie)

Neutron stars are born in core-collapse supernova (CCSN) events, and, along with black holes, are one of the most compact objects in the Universe. Magnetars are a class of neutron stars that have very strong magnetic fields, of the order of 10^{15} G at the surface, and a slow rotation period, between 1-12s. In the inner crust of neutron stars, i.e., cold β-equilibrium stellar matter, light and heavy (nuclei) clusters may exist. These structures could also form in warm nuclear matter with fixed proton fraction, such as CCSN matter, and neutron star mergers. Light clusters might have an effect on the average energy of both neutrinos and antineutrinos, emitted during the supernova explosion, as they may increase or decrease it, having thus consequences on the cooling of the proto-neutron star. Consequently, transport properties can also be modified by these inhomogeneities. In fact, the outer layers of a proto-neutron star have the ideal conditions for the formation of light clusters, especially tritons and deuterons, and these clusters are not always taken into account in the equation of state (EoS) for core-collapse supernova simulations. Another site where these clusters can form are heavy-ion collision experiments. These sites can have similar temperatures and densities as in CCSN matter, but the asymmetry and charge content can be quite different. Therefore, these terrestrial experiments can also be used to set constrains on warm nonhomogeneous matter. Besides terrestrial experiments, there are also astrophysical and observational constraints, like the 2 Msun pulsars PSR J0348+0432 and PSR J1614-2230. Therefore, the construction of unified EoS, constrained by all the possible data available, is the only way towards a better comprehension of these objects, which can have implications in the direct detection of gravitational waves (GW). The recent GW detection from the collision of two NS with the LIGO and Virgo interferometers, followed up by the gamma-ray burst GRB170817A and the electromagnetic transient AT2017gfo, set a new multi-messenger era for the astronomy, nuclear, gravitational and astrophysics community. NICER has recently published the first results of a NS mass and radius. ATHENA is expected to be launched in 2028, and SKA will be ready in the 2020's. FAST will give information on the NS mass. In this project, the candidate will construct an unified equation of state for magnetised stellar matter, which is the essential ingredient to build the stars' mass-radius relation, consistent with recent theoretical, experimental and observational developments, and which may advance our current understanding of compact astrophysical objects.

Vector Boson Scattering at the Large Hadron Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 1708 - Pedro Ferreira da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The observation of a Higgs boson by the ATLAS and CMS collaborations confirmed the standard model (SM) of elementary interactions. The presence of the Higgs boson with gauge couplings compatible with those predicted for the SM provides evidence that contributions from the exchange of this boson may be responsible for preserving unitarity at high energies. However, new phenomena may be present in the electroweak symmetry breaking (EWSB) sector, where a sensitive probe of new physics is naturally given by the study of the scattering of massive electroweak bosons (known as vector boson scattering, VBS) at high energy. Any deviation in the SM coupling of the Higgs boson to the gauge bosons breaks this delicate cancellation, thus permitting a test of the EWSB mechanism. The program proposed foresees the study of VVjj (V=W,Z) final states, produced in proton-proton collisions at the LHC via VBS. The study will be performed in the leptonic final states, including the tau lepton, in the decays of the V bosons. Thanks to the correlation between different final states and the inclusion of tau leptons, sensitivity to anomalous quartic gauge couplings can be significantly enhanced over the current results. The research will be carried out in the context of the Portuguese participation in the CMS experiment at the LHC, in the framework of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”. The candidate is expected to work in a team with a group of researchers.

Machine Learning and Measurements of the Higgs boson properties

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 144 - Joao Varela

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The subject of this thesis is the search for double Higgs production, decaying into taus and b-jets, at the Large Hadron Collider (LHC). The thesis is placed in the context of the Portuguese participation in the CMS experiment at the LHC, and it is linked to the Beyond the Standard Model (BSM) searches in the more general context of the searches for New Physics processes at the LHC. In the course of the last forty years, the SM has received increasing and consistent verification by precise experimental tests of its predictions, culminating in 2012 with the discovery of a new particle, which appears to be called “the” Higgs boson. There are, however, compelling reasons to believe the SM is not complete. In particular, the LIP/CMS group is engaged in the study of SM and BSM processes to fully exploit the opportunities of the unparalleled energy of the LHC collisions. A large amount of data of approximately 150/fb have been collected in Run1+Run2 and are available to study this process. With the upcoming Run3, additional 300/fb of data may become available in the next few years and there will be excellent opportunities for major discoveries in this domain. The work plan includes the study of the double Higgs production, each subsequently decaying to pairs of taus and b-jets. Advanced Machine Learning (ML) techniques will be used in the separation of signal and background events. The candidate is expected to work in a team with a group of researchers. Searches for new physics in this channel can be significantly improved with the additional data, and with improved analysis techniques. The research will be carried out in the context of the Portuguese participation in the CMS experiment at the LHC, in the framework of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”.

Effect of strong magnetic fields and rotation in the neutron star composition

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1709 - Helena Pais

Co-Supervisor: 174 - Constança Providência

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

Neutron stars, the remnants of core-collapse supernovae, are one of the most dense objects in the Universe, along with magnetars, neutron stars with very strong magnetic fields. In the neutron star inner crust, as the density increases, light and heavy (pasta) nuclei structures are formed, that can modify the neutrino transport, and have consequences in the neutron star dynamics and cooling. The strong magnetic fields on the magnetars surface are ~10^{15} G, and they have a slow rotation period, between 1-12 s. It was proposed that the lack of isolated X-ray pulsars, with a period higher than 12s, could be a direct indication of the existence of the pasta phases in the inner crust. Preliminary studies also indicate that the crust is more complex in the presence of a strong magnetic field. Unified equations of state (EoS), that describe NS from its outer crust to the inner core within the same nuclear model, are generally not available. The complete EoS is built out of three pieces: one for the outer crust, one for the inner crust, and one for the core, obtained from different models. Construction of unified EoS, constrained by astrophysical observations, like the 2 Msun pulsars PSR J0348+0432 [11] and PSR J1614-2230, and laboratorial experiments, is the only way towards a better comprehension of these objects, which can have implications in the direct detection of gravitational waves (GW). LIGO and Virgo have detected GW from the collision of two NS, which was then followed up by the gamma-ray burst GRB170817A and the electromagnetic transient AT2017gfo. NICER has recently published the first results of a NS mass and radius. ATHENA is expected to be launched in 2028, and SKA will be ready in the 2020's. The investigation of the effect of rotation and strong magnetic fields on the crust of neutron stars, taking into account the light and heavy clusters, and using a general relativistic approach with the publicly available LORENE code is the main goal of this project. Recently, a first calculation was already done, where the effect of strong magnetic fields on the structure of stars with 3 state-of-the-art EoS (nucleonic, hyperonic, and hybrid) was analysed, and relevant deformation is found for surface fields above ~10{16} G. We have considered poloidal magnetic field configurations for non-rotating stars. The joint effect of a toroidal magnetic field and rotation on the structure of neutron stars has been carried out before, and it was shown that neither purely poloidal nor purely toroidal magnetic field configurations are stable, and that stability requires twisted-torus solutions. In particular, the presence of a dominant toroidal component seems essential, for instance, to describe an increase of the inclination angle of a neutron star,as recent studies have shown. Therefore, in this the project, the candidate will explore a more complete description of magnetised neutron stars, which considers both toroidal and poloidal solutions. Such a calculation and the models presented will serve in the future as the initial data conditions for simulations of realistic EoS hydrodynamical mergers.

Towards a Yoctosecond Imaging tool of the Quark-Gluon Plasma

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 30 - Liliana Apolinário

Co-Supervisor: 172 - Nestor Armesto

Co-Supervisor: 1707 - Carlos A. Salgado

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: Mixed

Abroad-Institution: Universidade de Santiago de Compostela (IGFAE)

The study of the Quark-Gluon Plasma (QGP), a state of QCD matter characterised by extreme densities and temperatures, is at the forefront of the physics programmes of both the Large Hadron Collider (LHC) at CERN and the Relativistic Heavy-Ion Collider (RHIC) at BNL. Due to its very short lifetime, the assessment of QGP properties is only possible by relying on the probes that are generated within the collision. Among these, jets, a spray of highly energetic and collimated particles, are among the most widely used probes. Its production and evolution in proton-proton (pp) collisions are exceptionally well understood within the Quantum Chromodynamics perturbative approach. In the presence of a medium, however, the jet formation is known to be modified - a process generically known as jet quenching. By accurately assessing such modifications, jets have the potential to provide a unique tomographic analysis of QGP formation and evolution. Jet quenching description is still an on-going theoretical and phenomenological effort. As in pp collisions, the interpretation of heavy-ion collisions from heavy-ion collisions relies heavily on Monte Carlo event generators that are still under development. In this thesis, the student will contribute to the improvement of the jet-QGP interaction model and to further develop an existing jet quenching Monte Carlo based on perturbative QCD. The final result will be a cutting-edge tool able to provide a yoctosecond imaging of the QGP created in such collisions. This work will take place between LIP-Lisbon in Portugal (Liliana Apolinário) and the University of Santiago de Compostela in Spain (Nestor Armesto and Carlos Salgado).

New theoretical approaches in the context of LHC: increasing precision with 4-dimensional regularization methods

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 620 - Brigitte Hiller

Co-Supervisor: 1700 - Adriano Cherchiglia

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

The data collected and analysed at the Large Hadron Colider (LHC) do not point to significant deviations from the Standard Model (SM). To distinguish background (SM) from possible new contributions, it is paramount to develop stringent tests of self consistency of the SM. The calculation of cross sections beyond leading order in perturbation theory is important to compare with experimental data provided by particle colliders. Whilst computations at next-to-leading order (NLO) are standard and can be done in most cases in a fully automated way, at next-to-next-to-leading order (N2LO) and next-to-next-to-next-leading order (N3LO) calculations are considerably more complicated and only a small number of processes have been computed so far. Beyond leading order, QCD cross sections, for instance, are typically split into several parts. At NLO there are virtual and real corrections, at N2LO there are two-loop virtual, virtual-real and double real corrections. Virtual corrections involve the calculation of loop diagrams and only the sum of all contributions leads to finite results. Such contributions are usually ultraviolet (UV) and infrared (IR) divergent and usually regularization dependent. Gauge invariant dimensional regularisation (DR) is the standard possibility but it has a few drawbacks. It is not compatible with the helicity method and other computational techniques that rely on working in the physical dimension. This results in cumbersome expressions in intermediate steps of a calculation. This is particularly troublesome in higher loop calculations as computational programs need a clear separation of UV and IR divergences in order to evaluate cross sections, for instance. Therefore regularization methods that work in the physical dimension of the model are needed. Also, as established by the KLN theorem, there is a cancellation of divergences coming from the different sectors requiring that a significant part of the calculation must be done in analytical form. In this context, one is faced with the problem of choosing a regularization method to give sense to, otherwise, divergent quantities. A gain in efficiency could be depending on this choice, which justifies the interest in developing alternatives to the standard dimensional regularization scheme. In this project, we intend to tackle the infrared structure at N2LO in the Implicit Regularization (IReg) framework, which operates in the physical dimension and has been successfully applied to the computation of a cross section at NLO in perturbative QCD untangling ultraviolet and infrared divergences. For example processes of the type Higgs -> two gluons or Higgs -> heavy quark antiquark pair, or two gluon production in quark antiquark scattering are going to be considered in N2LO. As IReg operates in the physical dimension it is also a particularly useful tool for dimension specific theories, such as chiral and supersymmetric theories, where it has been largely applied. Given the emergence of different dimension specific approaches in recent years, we will explore the possibility of combining the most efficient strategies in a single approach. For instance IReg has a well developed procedure to isolate the UV content to arbitrary loop order. This line of research is supported by the Cost action CA16201 – Unravelling new physics at the LHC through the precision frontier, and FCT Project CERN/FIS-COM/0035/2019. Bibliography: --To d, or not to d : recent developments and comparisons of regularization schemes C. Gnendiger et al., Eur.Phys.J. C77 (2017) no.7, 471, and references therein. --Supercurrent anomaly and gauge invariance in the N=1 supersymmetric Yang-Mills theory, Y.R. Batista, B. Hiller, A. Cherchiglia, M. Sampaio, Phys.Rev. D98 (2018) no.2, 025018, and references therein.

Development of Resistive Plate Chambers offering simultaneous precise measurement of timing and two-dimensional position.

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1702 - Alberto Blanco castro

Co-Supervisor: 1714 - Custódio Loureiro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

Resistive Plate Chambers (RPC) are fast gaseous detectors traditionally used for trigger, e.g. in ATLAS and CMS, with a position and timing precision of several mm and 1 ns respectively and for timing measurements, e.g. in HADES and ALICE, with a time precision better than 100 ps. This is a consolidated and mature technology, which is commonly used in High Energy Physics (HEP) Experiments, especially when implementation over large areas is needed and an emerging technology in Astrophysics Experiments for Cosmic Rays (CR) measurements. The possibility to improve the position precision down to 100 um while keeping simultaneously the time precision at the level of 100 ps, implemented in large areas (1-2 m²) will be a major step for this technology. It could be used in particle identification (PID), by the time of flight (TOF) technique, in HEP experiments with clear advantages. The technique relies on the accurate measurement of the flight path and time by tracking and dedicated start and stop detectors respectively. By performing the measurements with detectors capable of measure simultaneously position and time each particle would be measured several times, improving timing accuracy (although on a shorter path), there would be no need for an external initial time detector, which is sometimes problematic and the cost would be reduced, since tracking would be performed at the same time with same device. Moreover, this technology would also have direct application in TOF Positron Emission Tomography (PET), where position and timing precision are crucial, in muon tomography where position precision is one of the most important parameters or in the emerging position sensitive neutron RPC detectors technology. The simultaneous measurement of position and timing with precision of 77 ps and 40 um, respectively, was firstly demonstrated by the LIP-RPC group in a small area (60 cm²) detector. Later, simultaneous position-timing measurements were also performed by other groups, however, the detector performance did not reach the level already demonstrated. Therefore, large position sensitive timing RPC capable to provide timing and position precision better than 100 ps and 100 um has yet to be demonstrated. The limitation factor to improve the position precision is not in the detector side, which has demonstrated already a position precision better than 100 um, but in the signal readout system, i.e. the RPC readout electrode configuration, the front end electronics (FEE) and the data acquisition (DAQ) system. Traditionally, in RPCs the readout is made by connecting a channel of FEE and DAQ to each of the strips used to read the signal induced by the detector. But due to the high number of strips needed to reach a resolution of 100 um over 1-2 m², this approach is not a possibility due to the high cost. Two alternatives can be explored. First one would be to connect each of the strips to a FEE and DAQ channel integrated in an Application Specific Integrated Circuits (ASIC), for this, an ASIC compatible with the signals generated by the RPC will have to be found and a system based on it will have to be designed. The second one would use some codification system of the signals readout from the strips to drastically reduce the number of FEE and DAQ channels needed. This thesis will be devoted to the study of these two approaches, with the design and construction of prototypes of RPCs and their readout systems and subsequent testing with cosmic rays or with particle beams.

Thermal evolution of hybrid stars

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 174 - Constança Providência

Co-Supervisor: 1474 - Violetta Sagun

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

The compact astrophysical objects, i.e. neutron stars (NSs), hypothetical hybrid (HS) and quark stars (QSs), are the most dense physical objects accessible by the direct observations. Despite the flourishing of astrophysical observations, the particle composition of the interior of compact stars is still very poorly known. Moreover, the physical processes inside hypothetical objects like HSs and QSs, for which is expected that matter goes through a phase transition from nuclear matter to a plasma of strongly interacting quarks, are also very poorly understood. Particularly, this limitation comes from the fact that QCD and its lattice formulation have very limited applicability at large baryonic densities and as such does not allow to obtain a reliable equation of state (EoS). Detection of QS or HS can become another scientific breakthrough and prove existence of quark matter, which is the main quest of largest research collaborations, such as ALICE at the Large Hadron Collider (LHC) in CERN. Compact stars cool down through a combination of thermal radiation from the surface and neutrino emission from the inner layers. Observational data on the surface temperature and the luminosity of stars provide with the valuable information about their internal composition, the EoS, the chemical abundances of the envelope and the degree, type and model of pairing of their constituent particles. Studying of the thermal evolution of compact objects with the quark core is the primary goal of the present research project. An existence of the quark-hadron phase transition, as well as other phase transition to a more dense phases of quark matter, will have an impact on the dynamics of the HS cooling. Their modeling can provide the community with an important opportunity to probe an existence and properties of phase transitions, as well as the EoS of strongly interacting matter at high densities. Another part of the PhD project will be dedicated to the study of the densest predicted phase on the QCD phase diagram, in which quarks can be paired between each other, and its impact on the thermal evolution of HSs. The thesis will be supervised by Constan\c ca Provid\^encia and Violetta Sagun, theoretical physicist, in the University of Coimbra

Phenomenology of heavy flavoured jet observables at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1705 - Joao Pires

Co-Supervisor: 1721 - Aude Gehrmann-De Ridder

Co-Supervisor: 92 - Helena Santos

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: Mixed

Abroad-Institution: ETH Zurich - Swiss Federal Institute of Technology in Zurich

In the Standard Model of particle physics, matter particles are arranged in two basic categories called quarks and leptons. The six quarks of the Standard model are paired in three generations – the up quark and the down quark form the first generation, followed by the charm quark and strange quark, then the top quark and bottom quark, which are the heaviest quarks. In proton-proton (pp) collisions taking place at the LHC, at high energies, the primary interaction involves partons, quarks and gluons, the latter being the mediators of the strong force governed by the theory or Quantum Chromodynamics (QCD). In the high energy stage of the collisions, those partons scatter and fragment producing a spray of highly energetic and collimated particles called jets which are detected as final states of the collision process. The observation of b quark-jets plays here a special role. Those are initiated by a b-quark at parton level and given their remarkable long lifetime, b-quarks decay at a secondary vertex significantly displaced from the primary collision, rendering the observation of b-quark jets in principle easier to detect in pp collisions than other types of quark or gluon jets. As a consequence, this property is used in an essential manner to disentangle final state b-jets from charm and light quark jets, generated from the first generation of quarks. In addition, this b-tagging procedure is a necessary experimental tool used to study physics processes with b-jets in the final state, such as Higgs decays to b-quarks (H->bb, HH->bbbb), top quark decays (t->Wb) and also in the search for heavier particles beyond the standard model decaying to b-quarks (X->bY). To compare the data on the related b-quark-jet observables with the corresponding theoretical predictions computed in the framework of perturbative QCD, a comparable b-jet tagging procedure needs also to be applied on the latter predictions. It is the aim of this thesis to understand inclusive b-jet production at the LHC from first principles by computing related jet observables in perturbative QCD including up to NNLO corrections in the strong coupling expansion. In particular we aim to look at (massless) bottom production, where the b-jet originates from a b-quark at parton level, and foresee to study the impact of NNLO corrections for phenomenologically relevant observables related to this specific jet production processes. To calculate such quark flavour sensitive observables at NNLO, the b-jet tagging procedure is highly non-trivial as it needs to keep track of the parton flavour in all parton level matrix elements involved at each perturbative order, before an infrared (flavour safe) jet algorithm, like flavour kT can be used to select the parton flavour sensitive jets. The selected candidate will apply this algorithmic procedure to calculate high-precision predictions using state of the art Monte Carlo generators and compare the results to LHC data, providing new insights into the mechanism of b-quark jet production in pp collisions. This work is expected to take place between LIP-Lisbon in Portugal (João Pires, Helena Santos) and the ETH Zurich in Switzerland (Aude Gehrmann-De Ridder). It is expected that the obtained results will be further used as a baseline to study b-jet production in heavy-ion collisions at the LHC, to further understand the energy loss mechanism of tagged b-jets in such collision systems.

Light Collection Array for Water Cherenkov Detectors

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 6 - Pedro Assis

Co-Supervisor: 13 - Bernardo Tomé

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

A giant, Large Field-Of-View, observatory of gamma-rays is being designed to be installed in the southern hemisphere. The observatory will consist of modular Water Cherenkov Detectors to sample the particles present in the shower initiated by gamma-rays in the atmosphere. To reduce the energy threshold several advanced techniques such as machine learning will be used for the reconstruction of the events. However, the energy threshold is directly connected with the quality of the Cherenkov light collection. The main parameters involved are the timing precision, the collection efficiency and the spatial resolution. This work is being developed in the context of an international collaboration, SWGO, and has as the baseline a matrix of sensors in the bottom of a white-painted water tank. In this work, it is proposed to study and develop a solution maximizing the capabilities of the detector. The main challenge is to have the best resolution with the best collection efficiency, minimizing the associated noise while being cost-effective. Solutions based on SiPM, with or without light-guides, scintillating or wave-length shifting materials are to be considered.

Dark-matter admixed compact stars and their properties under extreme conditions

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 174 - Constança Providência

Co-Supervisor: 1474 - Violetta Sagun

Co-Supervisor: 17 - Ilidio Lopes

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

Despite intensive searches for the particle nature of dark matter (DM) it still remains unclear. Until now, terrestrial experiments on nuclear recoil of DM, and direct searches of the DM annihilation have not yet found a suitable candidate. Because of it, the astrophysical probes of the DM properties are of high interest. Compact astrophysical objects, such as neutron stars (NSs) are especially attractive in this context, since they can accumulate a sizable amount of DM in the stellar interior. At the same time, depending on its nature, DM can affect the properties of NSs in quite different ways. For instance, An accretion of massive DM particles can significantly reduce the mass of the host NS, while light DM particles create an extended halo around the neutron star leading not to decrease, but to increase of its visible gravitational mass. At the same time, an accretion of self-annihilating DM to a NS will increase its luminosity and effective temperature. In addition, presence of the DM inside the NSs during their merger might produce a distinguishable signature in the GW signal, especially during the post-merger stage. The PhD project is devoted to study of an impact of the dark matter on properties of neutron stars, such as their mass, tidal deformability of matter, luminosity, effective temperature, etc. The main emphasis will be given to the astrophysical tests of the presence of DM and searches for the signals of its existence in compact stars. The selected candidate will establish a solid bridge between experimental and theoretical astrophysics, particle and gravitation physics. The thesis will be supervised by Constança Providência and Violetta Sagun, theoretical physicists, in Coimbra and Ilídio Lopes, an expert in astrophysics, in Lisbon.

Higgs couplings to light quarks

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Since the discovery of the Higgs boson at the LHC in 2012, by the CMS and ATLAS experiments, the focus has been placed in measuring its properties. In particular, on the determination of how it couples to the other standard model (SM) particles. In 2018, both CMS and ATLAS have detected the couplings of the Higgs to the heaviest quarks: the top (ttH) and the bottom (H->bb). The next big, and natural, step in this endeavour is to access the H couplings to the lighter quarks. The very high level of backround (light quarks are produced abundantly at the LHC, via QCD) renders the signals of direct Higgs decays to ligh quarks (H->qq) too tiny to be detectable with current data. But there's a catch (!): the quark-antiquark pairs originating from the Higgs decay may bind together (thus forming a meson state). Experimentally, this gives rise to a striking, clean signature: an energetic photon back-to-back to a dilepton resonance, H->Q+gamma. The Thesis project involves the search for such H boson decays to a quarkonium state and a photon, using the large dataset collected by CMS at the LHC. The motivation for the study is to experimentally constrain the Higgs-quark couplings, and help decide whether our new boson is indeed the particle at the heart of the SM, or (even more excitingly) a first particle beyond the SM. The thesis project involve the following possibilities: (i) increase the CMS analysis sensitivity by using the full dataset collected by CMS during LHC Run2; (ii) develop machine learning techniques for optimized selection, (iii) explore additional final states, specifically Jpsi and phi plus photon, which will probe respectively the couplings to the charm and strange quarks, (iv) work on the preparation of real-time selection algorithms (trigger), for gaining sensitivity to novel channels, to be deployed in the upcoming LHC Run3. The research will be carried in the frame of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”.

The Heavy Weights: Measuring Higgs and Top-Quark Associated Production at the ATLAS LHC Experiment to Probe Beyond the Standard Model

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 1720 - Yvonne Peters

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: Mixed

Abroad-Institution: University of Manchester

After an intense search, the associated production of the Higgs boson with a top quark pair was finally observed in 2018. This production channel provides the best way to directly measure the coupling between Higgs and top, the heaviest fundamental particles in the Standard Model (SM). But it also provides a way to look beyond the SM, in particular to search for signs of a non-standard Higgs boson, leading to CP-violation in the Higgs sector. Such a component is well justified in scenarios like the two-Higgs doublet model, and finding it would constitute a major discovery. In particular, it could lead to understanding why there is a huge asymmetry between matter and antimatter in the Universe. In this leading edge research, the selected student will analyze data collected by the ATLAS experiment during the LHC Run 3, to start in 2021. He or she will have the opportunity to participate in the operation of the experiment at CERN. The student will integrate the Portuguese ATLAS team and will use recent techniques developed in our group to enhance the experimental sensitivity of the analysis. He or she will be co-supervised by a colleague from the University of Manchester, where the student will spend part of the time of the PhD, as foreseen in the grant. Besides the Manchester group, the student would work in a vibrant international team within the ATLAS collaboration.

Particle Physics from Modern String Phenomenology

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 341 - Miguel Crispim Romão

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program:

Typology: National

Searches for Supersymmetry (SUSY) at the LHC have yet to find evidence for its TeV scale realisation. These, however, are focused on the so-called Minimal Supersymmetric Standard Model (MSSM), which is motivated by purely low-energy phenomenological studies and not only fails to address many questions, but it also raises new ones. A more satisfactory approach to SUSY will then address the shortcomings of the MSSM, as well as provide a framework with testable predictions at current and future colliders. Such is achieved by modern String Phenomenology, namely the recent developments on M- and F-theory regimes. In such regimes, the resulting SUSY models have strong UItra-Violet constraints over their parameters and symmetries, which define clear signals of their existence at current and future colliders. In this thesis we will explore the TeV scale consequences of these models. Namely, we will validate their validity in light of current LHC data. In addition to this, we will explore the implementation of Machine Learning techniques to scan the valid parameter space of such models in order to fully explore it.

Searching for new physics in the era of Deep Learning and Quantum Supremacy

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1713 - Felipe Ferreira de Freitas

Co-Supervisor: 1693 - António Morais

Co-Supervisor: 1722 - Alexandre Alves

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: Mixed

Abroad-Institution: Universidade Federal de São Paulo - UNIFESP

After the overwhelming success of the Large Hadron Collider (LHC) RUN-1 with the discovery of the Higgs boson, the RUN-2 halts with no evidence of Beyond Standard Model physics, raising concerns on whether or not the new physics lies at energies accessible to the LHC. In this scenario, the next LHC run, scheduled to start at the middle of 2021, brings up great expectations for both the Theoretical and Experimental Particle Physics communities. In this regard, an important aspect is the data collection and analysis. For instance, the RUN-3 of the LHC will produce 40 Tera Bytes of data per second to search for rare events, which after one year of operation translates to 5000 Peta Bytes, ~50 times the data generated by YouTube per year. The necessity to quickly process and analyze such a huge amount of information, in especial, for the use of artificial intelligence methods, in particular, Deep Learning, poses a challenge to data processing. Although the performance of Deep learning algorithms has greatly improved in face of the current development of General Purpose Graphics Processing Unit (GPGPU) and Field-programmable gate array (FPGA), this performance is quickly outshined when we compare it to quantum computers algorithms. The promise of quantum computers is that certain computational tasks might be executed exponentially faster than their classical counterparts. A fundamental challenge is to build a high-fidelity processor capable of running quantum algorithms in an exponentially large computational space, task that has been recently claimed by the Google AI Quantum team. In this thesis, we propose the exploration of Deep Learning algorithms, namely Deep Variational Autoencoders and jet-tagging algorithms tailored to use in quantum computers. These algorithms will have as main task the rapidly classification of events related to processes not expected by the Standard Model predictions, in particular rare events in the context of flavour physics and production of new exotic particles. We will make use of the most recent TensorFlow Quantum, a Python framework for hybrid quantum-classical machine learning that is primarily focused on modeling quantum data. This framework allows one to build Quantum Deep Learning algorithms and test them on a simulation of quantum computers using classical computer hardware. As concrete example of the type of New Physics scenarios that will be studied with the described techniques are heavy boosted Higgs bosons at the LHC. These particles are predicted in theories where the breaking symmetries beyond that of the Standard Model gauge group are concerned. A particularly attractive and rather novel framework is based on a trinification Grand Unified Theory (T-GUT) supplemented by a gauge SU(3) family symmetry. This framework is inspired by an embedding into E6xSU(3) and features an unique three Higgs doublet scalar sector at the electroweak (EW) scale. Such a Higgs sector is well defined and by no means arbitrary resulting from an unification with ordinary matter at very high energy-scale. As a byproduct of this construction, hierarchies in the light fermion spectra and quark-mixing consistent with those observed in nature are automatically emergent. In essence, a thorough study of boosted Higgs at the LHC can shed light on the details of a more fundamental description of particles and interactions. With this thesis we aim to build algorithms capable of running in the next generation of quantum computers and significantly increase the speed of data analysis processing, a crucial key for the next LHC runs and for New Physics phenomenology studies.

Exploring new physics scenarios and possible hints of Grand Unification at the LHC in the era of Deep Learning

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1693 - António Morais

Co-Supervisor: 1713 - Felipe Ferreira de Freitas

Co-Supervisor: 1723 - Roman Pasechnik

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: Mixed

Abroad-Institution: THEP Group - Lund University, Sweden

Despite the tremendous success of the Standard Model (SM), it is unquestionable that there are overwhelming phenomenological evidences that strongly suggest the need for a more complete theory. In particular, the existence of dark matter (DM), from galaxy rotation curves and anisotropies in the Cosmic Microwave Background, is becoming increasingly favoured by a particle physics explanation that the SM cannot offer. This follows from recent observations of the bullet cluster that show a dramatic offset between the visible plasma and the gravitational potential inferred from lensing, disfavouring, for instance, a modified gravity solution. The discovery of flavour oscillations between different neutrino species implies a quantum superposition of mass eigenstates, revealing another caveat of the SM where neutrinos are purely massless. Therefore, any complete, anomaly-free, beyond the SM (BSM) framework needs to account for, at least, three right-handed neutrino families. Last but not least, current B-physics as well as the electron and muon g-2 anomalies, whether fully or only partially confirmed by future data, may provide yet another strong hint for new physics beyond the SM. While the properties of the SM are remarkably well measured, a common explanation for its flavour and gauge structures is still lacking. With this thesis we propose a more fundamental first-principles approach capable of tying together the Higgs and matter sectors as well as flavour physics and Grand Unification, which are typically treated in different footings. A particularly attractive and rather novel framework is based on a trinification Grand Unified Theory (T-GUT) supplemented by a gauge SU(3) family symmetry. This framework is inspired by an embedding into E6xSU(3) or, possibly, into E8, the unifying force, and features an unique three Higgs doublet scalar sector at the electroweak (EW) scale where hierarchies in the light fermion spectra and quark-mixing consistent with those observed in nature are automatically emergent. As a byproduct, the low energy limit of the T-GUT framework offers well defined and by no means arbitrary phenomenological ingredients that need to be studied in coming years. In particular, the most distinctive prediction of this model consists of 2, down-type, singlet vector-like quarks (VLQ) and 3 doublet vector-like lepton (VLL) generations not far from the TeV scale and at the reach of the LHC or future colliders. Furthermore, it follows from the unification picture that the mass spectrum of such vector-like fermions are directly related to the ultra-violet limit of the model and a potential discovery could be regarded as a hint of a more fundamental theory. Finally, an extended neutrino sector can contain a sterile state that may play the role of a DM candidate. With this project we will look for answers to the following questions: 1) what is the nature of DM? 2) how is the Higgs sector consistent with flavour observables? 3) which particular VLQ and VLL signatures are expected and how can they provide hints of the unification picture? 4) and how can potential B and g-2 anomalies be addressed? The techniques we aim to develop in order to address the above questions will involve optimization algorithms based on Evolutionary searches for Deep Learning and Machine Learning tools. As a novel application, we intend to use such techniques as a “control” environment for Monte-Carlo event generator software, such as MadGraph, Pythia and MicrOmegas, in combination with model building tools such as SARAH and Feynrules.

Disentangling and Quantifying Jet-Quenching With Generative Deep Learning

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 341 - Miguel Crispim Romão

Co-Supervisor: 107 - José Guilherme Milhano

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

At very high energies or densities, quarks and gluons can produce a new state of matter known as Quark-Gluon Plasma (QGP), which is observed in heavy-ion collisions at modern colliders. Due to the non-perturbative nature of Quantum Chromodynamics (QCD), which is responsible for the interactions and dynamics of quarks and gluons, it remains a challenge to fully describe the QGP. One way of probing its nature is to study the properties of jets initiated inside the QGP medium with which they will interact at early times, a phenomenon known as Jet-Quenching. The interaction between a jet and the QGP will considerably change the jet properties and characteristics when compared to jets initiated in the vacuum, such as those happening in proton-proton collisions, making quenched jets an ideal probe into the QGP. In this thesis we will explore data-driven methods to explore the characteristics of quenched jets. Of particular interest, we will focus on recent developments of generative methods, such as Generative Adversarial Networks, which can harness the underlying statistical distribution of the data with a lower-dimensional statistical parameterisation, called latent space. In this space, we will be exploring how we can identify the degrees of freedom responsible for the phenomenon of Jet Quenching, and quantify it. For this, we will perform a detailed study of how the latent space variables relate to global and substructure jet observables, which are better understood from a QCD perspective, helping us to connect purely data-driven quantities with theoretical efforts.

Probing the primordial quark gluon plasma

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Quarks are known to loose energy as they traverse the hot and dense soup of quarks and gluons (QGP) produced in ultra-relativistic heavy-ion collisions at the LHC. b-quarks are particularly interesting to study, as they are produced early in the collision and thus experience the full evolution of the hot QGP medium. Up until recently, these crucial energy-loss mechanisms have been studied by measuring "jets" of particles (i.e. "jet quenching"). The exceptional capabilities of the CMS detector (in particular the muon and tracking systems) make it possible to identify and fully reconstruct b-quark states for the first time ever in collisions involving heavy ions. The aim of the Thesis project is the detection and study of b-quark hadrons in heavy-ion collisions (with particular the focus on the still-to-be-detected B0 meson and the rarer Bc meson). These novel probes facilitate unique information on the flavor and mass dependence of energy loss of particles that traverse the medium, and on underlying quark-recombination mechanisms yet to be observed at these scales. The Thesis project aims at making unique contributions to further our understanding of the primordial medium, by exploring novel probes and unprecedented energies at the LHC. The Thesis project involves the analysis of datasets collected by the CMS experiment in heavy-ion and proton-proton collisions at the LHC. The project is developed within the CMS working group formed by LIP and MIT teams.

Calibration control and monitoring of neutrino detectors

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1487 - Nuno Barros

Co-Supervisor: 267 - Francisco Neves

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The DUNE experiment is a next-generation long baseline neutrino experiment with a rich physics program including long-baseline neutrino oscillations, nucleon decay and atmospheric neutrinos. The experiment will use liquid argon time projection chambers (TPCs) technology, which allows to obtain large detectors with excellent tracking and calorimetry. To guarantee a precise 3D reconstruction of the physics events, it is necessary to have a detailed understanding of the detector conditions. For this reason, the DUNE collaboration has put in place a comprehensive calibration program including study of specific physics events, such as cosmic ray muons, but also using external calibration hardware like intense UV ionisation beams and dedicated radioactive sources. This project aims to implement a custom built dedicated electronics system that will permit to control the calibration hardware, and act as an interface with the data acquisition system (DAQ), monitoring and run control. This will involve the design and implementation of the electronic hardware, firmware and associated software interface. This effort will be complemented with the implementation of efficient data selection and monitoring algorithms to minimize the dead time imposed by the calibrations and optimise the quality of the calibration data taken. At a later stage, it is foreseen to leverage the experience acquired in previous activities to participate in the calibration data taking and analysis activities of ProtoDUNE run II. The project will initially focus on the development and implementation of the system in the context of the ProtoDUNE prototype at CERN, where the calibration systems will initially be deployed in 2021, with data taking expected to start in 2022. Using the experience from the ProtoDUNE data taking, it is then expected to project optimisations for the future DUNE far detector.

Search for New Physics in the associated production channel of a Higgs and a W boson at ATLAS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 55 - Patricia Conde Muino

Co-Supervisor: 220 - Rui Santos

Co-Supervisor: 1726 - Valerio Dao

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: Mixed

Abroad-Institution: CERN

Since the discovery of the Higgs boson, the precise measurement of its properties has become a fundamental part of the ATLAS Physics programme. The recent announcement of the observation of the Higgs decay to b-quarks and the associated production of the Higgs with top quarks, done by the ATLAS and CMS collaborations at CERN, probe directly the coupling of the Higgs to quarks and constituted an important step forward in the understanding of the Higgs mechanism. As the LHC continues to take data and more luminosity is accumulated, more precise measurements of the Higgs boson properties are possible, opening the door to search for new physics in the Higgs sector. Along this line of research, the study of the high transverse momentum (high-pT) Higgs production, in the associated production channel with a W boson, is sensitive to new physics in the hWW vertex and constitutes one of the measurements to be done in the near future by the ATLAS collaboration. The main objective of this research project is to search for anomalous Spin and CP components of the interaction vertex between the Higgs and the W bosons. The measurement will be done in the associated production channel of the Higgs with a W, when the W decays to leptons (𝓵𝜈) and the Higgs decays to b-quark pairs. Being affected by different systematics and kinematic constraints with respect to the h→WW decay, this channel allows probing the spin and CP properties of the hWW vertex in a complementary way to the studies done so far. The work plan foresees the identification of the most sensitive observables for anomalous couplings, followed by the analysis of the full Run-2 ATLAS dataset. The results will be interpreted in the framework of the Effective Field Theory (EFT) approach. At the same time the results will be interpreted in terms of extensions of the Standard Model with extra sources of CP-violation. The student will be part of the ATLAS team participating in this analysis. The work will be developed in an international collaboration and the results obtained will be presented at CERN. The student is expected to contribute in addition to the data taking and detector operation activities, both at CERN and at LIP. This PhD grant foresees a two-year stay at CERN to develop the proposed research project.

Causality in Lorentzian CFT’s

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 152 - Miguel Costa

Co-Supervisor: 85 - Vasco David Fonseca Gonçalves

Host Institution: CF-UM-UP - Centro de Física das Universidades do Minho e do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

Causality constraints in a QFT are associated to the Lorentzian signature of the theory. Since any unitary, Lorentzian invariant and causal theory can be analytically continued from the Lorentzian to the Euclidean signature, it is natural to ask what properties are necessary in the Euclidean version of the theory for it to be causal. This problem has been studied for unitary CFTs and for the particular case of a four-point function. It was found that in order to have a causal theory in the Lorentzian theory, the OPE coefficient between the two external operators and the lowest twist operator exchanged in the conformal block decomposition needs to be positive. The derivation exploits the analytic structure of both correlation functions and conformal blocks. It is usually the case that the lowest twist operator flowing in the conformal block decomposition is the stress tensor, so it is expected that these results are important in the context of dual Anti De-Sitter gravity theories. Indeed, a similar problem was also considered in the context of large N CFT’s that are dual to weakly coupled gravity in Anti De-Sitter space. It was found that non-minimal couplings are suppressed for theories with a large gap for higher spin operators above the energy-momentum tensor. In the dual language this restricts the OPE coefficients involving the energy-momentum tensor that are associated to the non-minimal couplings. It gives a constraint in this Euclidean data of the CFT, by imposing that such OPE coefficients scale with specific inverse powers of the gap. These results have then been shown from purely CFT arguments, by considering the Regge limit of four-point functions in such large N CFT’s. In the Regge limit a four-point function can be defined in terms of a phase shift whose imaginary part is positive. Such positivity follows from CFT first principles, while in AdS it implies unitarity in the sense that there no time advances. This is a beautiful demonstration of AdS causality from general CFT first principles. It therefore natural to ask what happens in the context of higher point functions. Can one impose new constraints on Euclidean data that arise from Lorentzian causality constraints? In this thesis we propose to explore many of the tools that are necessary to be developed in order to address this question.

UHECR Physics with the Pierre Auger Observatory

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 109 - Lorenzo Cazon

Co-Supervisor: 29 - Ruben Conceição

Co-Supervisor: 6 - Pedro Assis

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The Pierre Auger Observatory (formed by ~500 Physicists from ~90 Institutions) was built to study ultra-high-energy cosmic rays (UHECR), their origin and nature, as well as to study particle interactions at ultra-high energies. The main goal of this proposal is the participation in Auger, focusing on data analysis, shower and hadronic physics, where the group has recognized expertise, and to study the implications of our findings in the interpretation of the UHECR big picture. The Auger Observatory has completely reshaped the UHECR field, having established a flux suppression of the cosmic ray flux at energies above 55 EeV unambiguously and discovered that the highest energy cosmic rays have an extragalactic origin. These results support scenarios where particle acceleration takes place in sites distributed similar to the matter distribution in the Universe, with the energy losses due to the interaction with the Cosmic Microwave Background (CMB) leading to the flux suppression (called GZK cutoff) and arrival direction anisotropy. However, data on composition sensitive observables - using hadronic interaction models tuned with recent LHC measurements - require a radically different interpretation. It seems that the upper end of the cosmic ray energy spectrum is dominated by heavy particles from nearby sources for which the upper limit of acceleration almost coincides with the GZK energy. There are strong indications that hadronic interactions involved in Extensive Air Shower (EAS) are different from our expectations. Measurements show an excess of muons in EAS. that cannot be reproduced with current interaction models. The muon production depth has also been shown to have a significant discrepancy to the expectations. Understanding the origin of this inconsistencies is of great importance to break the degeneracy between primary composition and hadronic interactions models and thus solve the puzzle of UHECR. The primary scientific questions to be addressed are: a) the differentiation between the maximum energy of nearby astrophysical sources scenario and the GZK-cutoff, b) the determination of the mass composition, which is critical to understand the flux suppression, the nature of the sources and acceleration mechanisms, and c) understanding EAS andhadronic interactions at ultra-high energy. This project is mainly focused on understanding the shower physics and hadronic interactions within the air shower, with a two-fold goal. On the one side, this opens the opportunity to explore particle physics in phase-space and energy regions beyond the reach of human-made accelerators and act as a pathfinder for future accelerator experiments. On the other hand, the dominant uncertainty in the mass determination of UHECR is inherited from the uncertainties in the description of hadronic interactions. Reducing this uncertainty is crucial to solve the puzzle of UHECR origin, and to open the way to charge particle astronomy. The experimental study of the muonic component of the shower constitutes one of the most effective ways to infer properties of hadronic interactions: the distribution of the muon number at the ground, with particular focus on its fluctuations, the Muon Production Depth (MPD), and EAS muon energy spectrum will be analyzed. There is substantial effort to experimentally access the EAS muon component at the highest energies, with the Auger Upgrade, and also at the lowest energies with AMIGA (buried scintillators) and MARTA (LIP based project, CERN/FIS-PAR/0034/2019 in this call, using RPC’s beneath the Auger Cherenkov tanks). These new experiments pose new opportunities to understand the EAS muon distributions with higher accuracy and better control of systematic uncertainties. On the phenomenology part, our group has demonstrated that the shower-to-shower fluctuation of the number of muons is mainly sensitive to the multiparticle production properties in the first interaction. For proton primaries, the muon number distribution displays an exponential tail that depends solely on the spectral features of the highest energy neutral pions that emerge from the first UHECR interaction with air. Within this project, the possibility of such novel measurements will be explored. Accessing such quantities would allow the constraint of the multiparticle production at the highest energies, in particular, the energy flow to the EM sector.

Signals from Beyond: Search for Anomalies in the LHC Data with the ATLAS Experiment at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1717 - Rute Pedro

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program:

Typology: National

The Standard Model (SM) of Particle Physics is notably descriptive and predicted new particles well in advance, from which the Higgs boson discovered at CERN's Large Hadron Collider (LHC) is a remarkable recent case. However, there is paramount evidence for the need of beyond-Standard Model (BSM) physics, namely to provide dark matter candidates, explain the matter/dark-matter asymmetry, address the hierarchy problem and others. The LHC has a rich program on searches for New Physics (NP) but clues from new particles or interactions have not yet been located. Typical searches are guided by specific BSM candidates and would benefit from a complementary model-independent strategy, augmenting the scope of searches to signs of NP not even framed by theory. This proposal is to perform a novel generic search for NP within the ATLAS/LHC experiment using anomaly detection (AD) techniques based on generative Deep Learning (DL). The DL model will learn SM physics from simulated data and then look for anomalous non-SM like events in the real collision data. Detector effect anomalies can mislead the NP detection and a detailed study of this background will be considered to construct a high fidelity AD. Moreover, the impact of sources of theoretical and experimental uncertainties on the AD performance will be assessed. Benchmark NP signals will be used as tests throughout the AD development. The project will be integrated into the ATLAS Portuguese group, and collaboration with several international groups is foreseen. Synergies with the LIP Competence Centre for Simulation and Big Data and with the LIP Phenomenology group will be explored, namely to investigate approaches for experimental result interpretability and recasting into theory exclusion limits.

Global Analysis of Top Quark Couplings at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1728 - Antonio Onofre

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program:

Typology: Mixed

Abroad-Institution: CERN

A novel approach to carry out global analyses of the top quark couplings at the LHC, within the Standard Model Effective Field Theory (SMEFT), is proposed in this PhD thesis. The global analysis includes studying several production and decay channels from top quark double production, top quark single top production and associated production of top quarks with gauge bosons, ttX (X=gamma, Z, W and Higgs ), globally. Final states with one, two or three charged isolated leptons will be selected for the RUN 3 of the LHC, using data from the ATLAS experiment. The HEP-Frame analysis framework (similar to MadAnalysis 5), developed by the team, will be used to perform the global analysis. New angular distributions are expected to be studied, from the phenomenological point of view, for the global analysis. Results will be interpreted in terms of the Wilson coefficients, within the SMEFT framework.

Development of fast parallel trigger algorithms for the ATLAS experiment at CERN

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 55 - Patricia Conde Muino

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The LHC is the highest energy particle accelerator ever built. The gigantic ATLAS experiment records proton and ion collisions produced by the LHC to study the most fundamental matter particles and the forces between them. At the nominal rate of the LHC, the proton bunches cross 40 million times per second, producing up to 40 collisions per bunch crossing. This event rate is processed in real time by the ATLAS Trigger and data acquisition system, that analyse the results of the collisions, as registered by the 10^8 electronic channels of the detector to select a maximum rate of about 1000 events/second for further offline storage and analysis. In 2025-26, the LHC will be upgraded to increase the LHC collision rate up to a factor 7, to allow acquiring a huge amount of data and pushing the limits of our understanding of Nature. The collision rate and data volume after the LHC upgrade will impose extreme demands on the ATLAS trigger system. The estimated increase in trigger rates and event size lead to larger data volume and much longer event reconstruction times, that are not matched by the slower expected growth in computing power at fixed cost. This requires a change in paradigm, increasing parallelism in computer architecture, using concurrency and multithreading and/or hardware accelerators, such as GPUs or FPGAs for handling suitable algorithmic code. The objective of this thesis program is develop novel calorimeter clustering and jet reconstruction algorithms using accelerators such as FPGAs or GPUs, for the Phase II Upgrade of the ATLAS Trigger system. The student will work in close collaboration with researchers from LIP computing center and particle physics groups, as well as with colleagues from CERN and other institutions involved in the ATLAS experiment. This work will be developed in an international environment. The student will contribute to the improvement of the jet trigger system of the ATLAS experiment at CERN. Presentations at ATLAS Collaboration meetings are expected, either by video-conferencing or at CERN.

Distinguishing dark matter models at the Large Hadron Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 220 - Rui Santos

Co-Supervisor: 26 - Nuno Castro

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Although the existence of dark matter seems to be quite plausible, its nature is still a complete mystery. Models with fermionic, bosonic or scalar dark matter are possible and are presently in agreement with all experimental data. When dark matter is produced at colliders, it has to be produced alongside a visible particle, or it will be undetectable. Still, the missing energy in the collision, which could be a signal of dark matter, has to be understood in terms of the different models proposed. The goal of this work is to model this missing energy and to try to relate it with the theoretical models proposed. The work has both a strong theoretical and experimental components.

Neutron background in neutrino detectors

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 15 - Sofia Andringa

Co-Supervisor: 879 - Valentina Lozza

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Neutrino fundamental properties may be in the origin of the matter anti-matter asymmetry in the Universe and are being searched for in experiments with different detector technologies. Neutrons, produced by cosmic muon spallation or by alpha interaction on detector materials, are an important background for low energy neutrino analyses, such as the search for double beta decay, or the measurements of solar, geo and supernova neutrinos. The aim of this project is to quantify and reduce the main uncertainties for the prediction of neutron production rates, and to measure the corresponding cross-sections in auxiliary dedicated experiments and in two running neutrino experiments, SNO+ and ProtoDUNE.

Calibrating neutrons for DUNE

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 15 - Sofia Andringa

Co-Supervisor: 1487 - Nuno Barros

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

DUNE will search for CP-violation in the lepton sector by comparing neutrino and anti-neutrino oscillations over a baseline of 1300 km. Neutrons are produced in different numbers in the interactions of neutrinos and anti-neutrinos, degrading the energy resolution fundamental for the oscillation measurements. This project is focused on the identification of neutrons in the DUNE liquid argon detectors, using existing data of the ProtoDUNE detectors running at CERN. It will make use of an innovative pulsed neutron source, dedicated to the low energy calibration of DUNE, and delivering a large clean sample of neutron captures. This sample will be fundamental for the training of the reconstruction algorithms and neural network methods used to classify the detailed and complex images of each neutrino interaction delivered by the DUNE detectors.

Muon tomography with RPCs

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 15 - Sofia Andringa

Co-Supervisor: 13 - Bernardo Tomé

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Muography and muon tomography have received a significant boost in the last decade, and will soon leave particle physics institutes to be used in many applications. Recent developments in resistive plate chamber detectors have made them more robust and able to operate in non-laboratory environment. The project will be based in use cases with different challenges, with data taking by the same RPC-based telescope from the basement of a building and in an underground mine gallery. It will address the automation of the operation and data analyses, developing the tools for self alignment and calibration, data cleaning, image reconstruction and interpretation, aiming to deliver also an end-to-end product for external users of muography.

Search for new physics with forward proton detectors at ATLAS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 55 - Patricia Conde Muino

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The non-abelian structure of the gauge theory in the SM implies the existence of triple and quartic gauge boson couplings (TGC and QGC, respectively) fully constrained by the gauge symmetry. The measurement QGC provide a window into the Electroweak symmetry breaking mechanism, given the fact that the longitudinal modes of the W and Z bosons are Goldstone bosons. Deviations from the SM predictions can appear due to interchange of new particles, integrated out in the effective interaction, in new physics theories. Models with a new heavy scalar singlet interacting with the Higgs sector can modify the quartic gauge boson couplings but not the triple ones. It is, therefore, essential to probe this missing part of the SM, measuring both the TGC and QGC. 
  The ATLAS sensitivity to anomalous couplings in the γγWW, γγγγ and γγZZ vertices can be improved two orders of magnitude by using the ATLAS Forward Proton tagging detectors (AFP) [1]. AFP effectively converts the LHC into a photon-photon collider: the two scattered protons emit two photons that annihilate to produce a pair of vector bosons (two W’s, for instance). The protons, that stay intact after the interaction, are scattered through very small angles and they are detected at the AFP stations. Since there is no underlying event, the two vector bosons are the only particles produced centrally. If they decay to leptons they can be easily triggered and identified. The invariant mass of the vector boson pair can be measured precisely by determining the proton energy loss with the AFP detectors, even in the case of neutrinos in the final state. The presence of anomalous quartic gauge boson couplings could be observed as an increase in the number of detected vector boson pairs with large invariant masses. This project proposes the search for anomalous couplings of the type γγWW using the AFP detectors. The same final state can be used to search for dark matter in photon-induced processes, using also the capability of the forward proton tagging detectors [2]. The search for dark matter is challenged due to the low transverse momentum of the leptons produced. An adequate strategy for triggering this kind of processes is therefore needed. It implies the combination of proton tagging information with muon/electron triggers reconstructed with the ATLAS central detectors, already at the first level trigger and probably making use of the topological trigger processors. The development and optimisation of such a trigger strategy is also an objective of this project. The student is will develop the work in the framework of the ATLAS international collaboration. S/he is expected to contribute to the ATLAS data taking activities and also the commissioning and performance studies of the AFP detector, fundamental for the success of this project. Frequent presentations of the results achieved are expected, either in collaboration meetings at CERN or by videoconference. 7.- References [1] E. Chapon, C. Royon, and O. Kepka, Anomalous quartic WWγγ, ZZγγ, and trilinear WWγ couplings in two-photon processes at high luminosity at the LHC, Phys.Rev. D81 (2010) 074003, arXiv:0912.5161 [hep-ph]. [2] L.A. Harland-Lang, V.A. Khoze, M.G. Ryskin and M. Tasevsky, LHC Searches for Dark Matter in Compressed Mass Scenarios: Challenges in the Forward Proton Mode, arXiv:1812.04886 [hep-ph]

Jet quenching: bridging theory to experimental data

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 30 - Liliana Apolinário

Co-Supervisor: 1711 - Leticia Cunqueiro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: Mixed

Abroad-Institution: CERN

Heavy-Ion collisions are an important part of the current and future physics program of high energy colliders. In particular, the Large Hadron Collider (LHC) at CERN is now preparing future upgrades to increase luminosity and centre-of-mass energy. For heavy-ions, this will unlock novel measurements to study the new state of hot and dense matter to believed to be part of the early stages of our Universe: the Quark-Gluon Plasma. Among the possibilities to study its properties and evolution, hard probes, such as jets (spray of high momentum particles that are the result of the fragmentation of a high momentum quark or gluon) have shown a massive potential in unveiling the QGP properties. In particular, it opened the first exploration avenue for QGP tomographic analysis. In this thesis, the student is expected to engage on a phenomenological study to constrain the analytical description of the medium-induced modifications that a jet experiences when travelling through the QGP - a process known as jet quenching -, and ultimately to measure the QGP properties and its time evolution. This study will be at the forefront of current efforts, comprising a strong theoretical and phenomenological approach (such as design of novel observables, development of jet quenching Monte Carlo event generators, among others) to bridge current jet quenching models to experimental data, with a particular focus at the LHC. For that, the student will be co-supervised by Liliana Apolinário (at LIP) and Leticia Cunqueiro (at CERN, member of the ALICE collaboration), benefiting from close collaboration with both theory and experimental communities of Portugal and CERN.

Constraining dark matter in Nature's own dark matter laboratory

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1727 - Jarle Brinchmann

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

Ultra-faint dwarfs are the faintest galaxies we know, and they are also the most dark matter dominated structures we know with dark matter outweighing normal matter by up to 1000:1, making them ideal "laboratories" for studying dark matter. This project builds on 100hrs of telescope time on the ESO Very Large Telescope (PI Brinchmann) to observe a sample of 10 ultra-faint dwarfs (UFDs) with the MUSE integral field spectrograph (see Zoutendijk et al 2020 for first results from this program). The aim of this survey is to use the stars in the UFDs as test particles in the dark matter potential to infer the dark matter content and crucially the dark matter density profile in these systems. In massive dwarf galaxies the density profile is found to have a central core, while cold dark matter generically predicts a cuspy central density profile. In the more massive dwarfs this difference can be explained by baryonic effects, but in UFDs the continued existence of a core would indicate a deviation from cold dark matter. In this project, the student will be responsible for reducing the data from MUSE for those UFDs not yet reduced, extract spectra of stars, measure their velocities and build a dynamical model for each dwarf. A key challenge will be to develop a methodology to jointly analyse multiple UFDs to place the strongest possible constraints on the nature of dark matter using the UFD density profiles. Alongside this, the student will also identify binary stars in the UFDs and develop ways to minimise their impact on the dynamical models as well as develop the first census of binary stars in faint dwarf galaxies, a thus far almost completely unexplored area. Finally, the student will put constraints on axion dark matter by searching for possible emission lines from axion-2 photon coupling in the MUSE datacubes.

Exploration of hadronic interaction properties with the MARTA Engineering array

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 29 - Ruben Conceição

Co-Supervisor: 982 - Raul Sarmento

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Nature and arrival direction of cosmic rays at the highest energies can only be inferred indirectly through the analysis of the air shower induced by their interaction with the atmosphere. The understanding of the shower development relies on our knowledge about the hadronic interactions that can occur at energies well above those reachable at accelerators on Earth. Muons, being long-lived particles, carry essential information about these hadronic interactions that rule the shower development. Therefore, their detection at the ground is a crucial tool to understand the physics of extensive air showers and particle interactions at extreme energies. However, the measurement of the highest energy extensive air-showers and in particular of the produced muons poses several challenges as it has to be performed in an outdoor environment, using detectors covering a vast area. The LIP group is leading the MARTA project, which proposes an innovative concept for the muon detection in air-shower experiments. MARTA (Muon Array of RPCs for Tagging Air showers) uses an innovative technique to measure the shower muon component directly. It uses the standard water Cherenkov detector, which is sensitive to all shower components, as an absorber to the electromagnetic shower component. Resistive Plate Chambers, placed below the water tank, with a high segmentation and time resolution, can then be used to measure muons. Several full-scale MARTA prototypes are already installed and taking data in the Pierre Auger Observatory - currently the biggest cosmic ray observatory in the world - situated in Argentina. In particular, the MARTA Engineering Array (EA), consisting of seven MARTA stations, is planned to start to be deployed in Auger during 2020. This array will measure the muons on an event-by-event basis and will collect shower events produced mainly at centre-of-mass energies compatible to those reached currently at the Large Hadron Collider, LHC. Hence, MARTA EA data analysis will provide not only strong tests to the shower hadronic physics but also its successful operation would pave the construction of future hybrid cosmic ray experiments. The selected candidate will be involved in the activities of the LIP/Auger group, in particular: Participation on the commissioning of the MARTA Engineering Array; Validation of the detector concept and performance; Development of data analysis tools to reconstruct showers; Extract information from the showers using the MARTA EA and combine it with LHC to further constrain hadronic interaction properties.

Measurement of top quark rare decay t->sW at ATLAS

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 140 - Filipe Veloso

Co-Supervisor: 484 - Ricardo Gonçalo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

The top quark is the heaviest elementary particle known, with a mass close to the electroweak symmetry breaking, and it can provide clues about the symmetry breaking and the Higgs mechanisms. It is thus an excellent object to test the Standard Model of Particle Physics (SM). There is an important effort to study the top quark properties, like its mass, production cross-sections, electric charge, spin, decay asymmetries, rare decays, etc... Deviations from SM predictions of the production and decay properties of the top quark provide model-independent tests for physics beyond the SM. According to the SM, the top quark decays nearly 100% of the time to a W boson and a b quark. The Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix is related to the rates of the Flavour Changing Charged Current (FCCC) decay modes. Some of the elements, e.g. Vts, were not yet directly measured but are determined from the unitarity conditions of the matrix. A direct measurement of these elements put strict conditions on the assumptions behind the matrix properties, as the existence of only three families on the SM. This research program will be developed within the Portuguese ATLAS group. It aims to measure the decay rate of the top quark into a W boson plus a s-quark with LHC data collected by the ATLAS detector using computational tools such as machine learning techniques. This result will then be used to measure the amplitude of the CKM element Vts. In addition the student will participate in the maintenance and operation of the ATLAS detector, namely in the calibration of the TileCal hadronic calorimeter. Short periods at CERN may also be required in order to collaborate in working meetings and/or shifts.

Searching for the rarest decays in the Universe

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 464 - Alexandre Lindote

Co-Supervisor: 617 - Claudio Frederico Pascoal da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

The rarest nuclear process ever observed in laboratory is the double electron capture (2𝜈2EC) in Xe-124 [1], with a half-life of 1.8x10^22 years (10^12 times longer than the age of the Universe). In this Standard Model allowed process, the nucleus captures two orbital electrons and emits two neutrinos (Xe-124+2e− → Te-124+2𝜈e). The LUX-ZEPLIN (LZ) detector [2] will start operating in early 2021, and with a total of 10 tonnes of xenon can claim a >5σ discovery for this decay after just a few months of operation. Moreover, with the energy available from its high Q-value, this isotope can have two additional and even more rare decays: the emission of two positrons (2𝜈2β+) and a mixed mode with the emission of a positron and the capture of an orbital electron (2𝜈ECβ+). Although the former is too rare to be detected by the current generation of detectors, the latter is expected to have a half-life of the order of 10^23 years and lead to a few hundreds of events in LZ in 1000 days, thus claiming the title of rarest process ever observed. Observation of all these decay modes will contribute valuable information to improve our current understanding of nuclear models. Neutrinoless modes of these decays can also occur if the neutrino is a Majorana particle (i.e., its own antiparticle), providing an interesting alternative access to the nature of the neutrino other than 0𝜈2β [3]. Although their half-lives are expected to be several orders of magnitude higher than that of 0𝜈2β, resonances may occur in which the close degeneracy of the initial and final (excited) nuclear states can enhance the decay rates by as much as 10^6. In particular the 0𝜈2EC from the LL-shell in Xe-124 can have a half-life as low as 10^24 years, leading to ~30 of events in LZ in 1000 days. In this project the PhD candidate will explore LZ data for these various rare decays, developing the required analysis tools and estimating the dominant backgrounds for each. This project also envisages the use of Machine Learning algorithms such as convolutional neural networks to explore the particular event topology of these decays, providing some efficiency to distinguish such decays from their main background. The observation of any of these decays will undoubtedly lead to a highly impacting publication. [1] Nature 568 (2019), 532–535 - "Observation of two-neutrino double electron capture in Xe-124 with XENON1T" [2] Phys.Rev. D101 (2020), 052002, arXiv:1802.06039 - "Projected WIMP Sensitivity of the LUX-ZEPLIN (LZ) Dark Matter Experiment" [3] arxiv:2002.04239 - "Detection prospects for the second-order weak decays of Xe-124 in multi-tonne xenon time projection chambers"

Particle-Astroparticle physics interplay in extensions of the SM

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 147 - Filipe Joaquim

Co-Supervisor: 110 - Ricardo Gonzalez Felipe

Host Institution: CFTP - Centro de Física Teórica de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

In spite of being a very successful theory, the Standard Model (SM) of particle physics is not able to explain all observed physical phenomena. In particular, besides not accounting for neutrino masses and mixing, the SM also fails at supplying a suitable dark-matter (DM) candidate, and a convincing explanation for the observed excess of matter over antimatter in the Universe. This thesis aims at studying theoretical frameworks where these three problems can be solved. Special emphasis will be given to beyond-the-SM scenarios with new scalars and/or fermions which, besides participating in the neutrino mass generation mechanism, also play a crucial role in the explanation of dark-matter and the matter-antimatter asymmetry of the Universe.

Probing the CP nature of the Yukawa Couplings of the Higgs Boson to Fermions at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 220 - Rui Santos

Co-Supervisor: 1728 - Antonio Onofre

Host Institution: CFTC - Centro de Física Teórica e Computacional

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The precise determination of the CP-nature of the discovered Higgs boson is an outstanding problem of the Standard Model (SM). Although the LHC experiments established the Higgs boson [1,2] cannot be a pure pseudoscalar with more than 99% confidence level (CL), a mixed state with a significant CP-odd component is still possible. The need for further sources of CP-violation was first discussed by Sakharov as one of the three conditions for baryogenesis to occur [3]. This is an important motivation to look for physics Beyond the Standard Model (BSM) and, in particular, to models with extra sources of CP-violation. One of the simplest extensions of the Standard Model (SM) we can build with a CP-violating scalar sector, is to add an extra scalar doublet to the SM field content while keeping the same gauge symmetries. The CP-conserving version of the model is commonly referred as two-Higgs doublet model (2HDM), while the simplest CP-violating version of the model is known as complex 2HDM (C2HDM) [4]. The CP nature of the Higgs boson couplings (kt,kb,kc and ktau) to heavy fermions (t, b, c and tau leptons) is addressed in this PhD thesis proposal, once they can be probed directly at the LHC. At low energy, the different flavor diagonal CP violating couplings are bounded by EDMs [5]. For the electron Yukawa, the latest ACME measurement results into an upper bound of κe<1.9×10^−3. Whereas for the bottom and charm Yukawas, the strongest limits come from the neutron EDM. Using the NLO QCD theoretical prediction, this translates into the upper bounds κb<5 and κc<21 when theory errors are taken into account. For the light quark CPV Yukawas, measurement of the Mercury EDM places a strong bound on the up and down Yukawas of κu<0.1 and κd<0.05 (no theory errors) while the neutron EDM measurement gives a weaker constraint on the strange quark Yukawa of κs<3.1 (no theory errors). LHC events from the production of heavy fermions accompanied by Higgs bosons (bH, bbH, cH, ccH and tautauH) will be probed with the major goal of measuring directly the CP-nature of the heavy fermions Yukawa couplings (kt,kb,kc and ktau), in a global approach. These studies complement in a very nice way, the expertise the supervising team has already in the search for ttH (associate production of top quarks together with Higgs boson) and their involvement in the measurement of the CP-nature of the top quark Yukawa coupling, either from the phenomenological point of view or the measurement performed at the LHC. As was done for the ttH process, the study of new angular observables, sensitive to the CP nature of the coupling, is expected to be performed. The role of observables evaluated in the centre-of-mass of the full system, as was done for the ttH production recently with significant gains in performance, will be explored for the new channels. While indirect measurements put quite strong bounds on CP-violation for the ttH channel, for the b-H, c-H or tau-Higgs Yukawa couplings, the limits are quite weak. This leaves room to test angular differential distributions developed for the ttH, from the phenomenological point of view, with a particular focus on the boosted regime, towards measurements intend to be performed during RUN 3 and the High Luminosity phase of the LHC (HL-LHC). The results are expected to be interpreted as well within the context of the 2HDM model, with explicit CP-violation. [1] ATLAS Collaboration, G. Aad et al., Phys.Lett. B716, 1 (2012), 1207.7214. [2] CMS Collaboration, S. Chatrchyan et al., Phys.Lett. B716, 30 (2012), 1207.7235. [3] A. D. Sakharov, Pisma Zh. Eksp. Teor. Fiz. 5, 32 (1967), [Usp. Fiz. Nauk161,61(1991)]. [4] T. D. Lee, Phys. Rev. D8, 1226 (1973); I. F. Ginzburg, M. Krawczyk, and P. Osland, Two Higgs doublet models with CP violation, pp. 703–706, 2002, hep-ph/0211371, [,703(2002)]; A. Barroso, P. M. Ferreira, R. Santos, and J. P. Silva, Phys. Rev. D86, 015022 (2012), 1205.4247; D. Fontes, J. C. Romao, R. Santos, and J. P. Silva, JHEP 06, 060 (2015), 1502.01720. [5] M. Cepeda et al. [HL/HE WG2 group], arXiv:1902.00134 [he

Enhancement of the measurement capabilities for the Pierre Auger Observatory

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 6 - Pedro Assis

Co-Supervisor: 109 - Lorenzo Cazon

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

LIP has been leading within the Pierre Auger Observatory, the development of a dedicated muon detector to develop the measurement capabilities of the Observatory, focusing mainly on the muonic component of Air Showers. Auger was built to give a significant contribution to the understanding of ultra-high energy cosmic rays (UHECR), their origin and nature, as well as to study particle interactions at such high energies. The data taken by Auger led to several breakthroughs in UHECR physics. A suppression of the CR flux above 5.5x10^19 eV is firmly established, and the fine structure of the spectrum starts to unveil. A dipolar asymmetry on the arrival directions has been observed, strongly supporting their extra-galactic origin. The CR composition at very high energies have been inferred from shower measurements, and its interpretation indicates an unexpected transition from proton to heavier elements above 3x10^18 eV. The collaboration has also a research program to estimate the hadronic interaction properties at the highest energies. One of the most intriguing results from this research area is the apparent muon deficit in predictions. Additionally, no hadronic interaction model can explain all the measured shower observables simultaneously. The obtained results present either an unexpected astrophysical panorama or even new physics at the highest energies. However, the above claim gets significantly undermined by the poor control over the shower description, i.e. over our understanding about hadronic interactions. This puts pressure on the study of the shower muonic component. Muons stem directly from the decay of charged mesons and can travel long distances being able to reach the ground. They are thus a direct link to the hadronic interaction activity within the shower. Auger has set up an upgrade program to increase the collected information for each shower. In this context, LIP is responsible for the installation of MARTA, a small array of RPCs under the WCD to perform a direct measure of the muons present at the stations. MARTA high quality data will enable cross-calibrations between different detectors and will be able to deliver physics muon measurements at E = 10^17 eV, which corresponds to the LHC centreof- mass energy. Such measurements would allow univocal tests to the performance of high-energy hadronic interaction models. The candidate will participate mainly in the comissioning of the MARTA detector, on its instrumentation and data-taking. Analysis of the data at station level and on its relation with data taken with other detectors will also be considered.

A next-generation gamma-ray observatory powered by machine learning techniques

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 29 - Ruben Conceição

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The observation of the high-energy gamma-rays provides a unique window to explore the extreme energy universe and fundamental phenomena related to it. The observation of these rare phenomena implies the construction of huge compact experiments, with areas of 100 000 m^2, placed at altitudes that surpass the 5000 meters above sea level. These experiments should be able to fight the enormous hadronic background to observe the gamma-rays. Classically, this has been done by identifying muons, which led to detector options which are unfit for such an ambitious project. New ideas to build a next-generation experiment are currently being assessed by the Southern Wide-field Gamma-ray (SWGO) collaboration. At LIP, we have shown that the application of Machine Learning algorithms together with innovative detector solutions, can lead to a smaller, more capable next-generation detector which could revolutionize the field of gamma-rays. In particular, the time evolution of the detector response can be exploited to identify the nature of the particle entering the tank. While very promising, the implementation of these neural networks has many challenges ahead: the complexity of the problem and necessity to perform features engineering; use of simulations with incomplete accurate descriptions; resilience to spurious effects (backgrounds)... This work will be developed in close collaboration with the computer science department of Granada University.

Collider and Gravitational probes for New Physics in Multi-Higgs Models

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1693 - António Morais

Co-Supervisor: 1713 - Felipe Ferreira de Freitas

Co-Supervisor: 1723 - Roman Pasechnik

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: Mixed

Abroad-Institution: THEP Group - Lund University, Sweden

With the recent observation of gravitational waves (GW) by the LIGO-VIRGO collaboration and the Large Hadron Collider (LHC) RUN-3 scheduled to start at the middle of 2021 with twice the nominal luminosity and a center of mass energy of 14 TeV, a great opportunity for New Physics searches following a multi-messenger philosophy has emerged. In particular, models with extended scalar sectors feature the possibility of first order phase transitions (PT) capable of generating a stochastic background of primordial GW which, if detected, can become a gravitational portal and a probe for Beyond the Standard Model (BSM) physics. The LISA mission will offer a range of frequencies well into the mHz region, relevant for the electroweak (EW) PT. The non-trivial structure of such extended scalar sectors allows for multi-step phase transitions and corresponding GW signatures. This information, in synergy with collider physics, can offer complementary information on the quest for hints of a more complete description of particles and interactions. In this thesis we will consider models with additional electroweak Higgs doublets and singlets, supplemented by additional flavour or gauge symmetries, whose breaking takes place not far from the EW scale. We will investigate which particular BSM signatures are expected at the LHC for different benchmark models and how can this information be complemented by the stochastic background of GW, with focus on the future LISA mission. We will also consider models where vector-like fermions, extended neutrino sectors as well as composite Higgs scenarios will be studied along the same research strategy. These studies involve the development of intelligent algorithms based on Evolutionary searches for Deep Learning and Machine Learning. Such techniques will be used as a “control” environment for Monte-Carlo event generator software tools, such as MadGraph, Pythia and CosmoTransitions.

Development of a high voltage system for the ATLAS Tilecal calorimeter and performance tests with high energy particles

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 305 - Guiomar Evans

Co-Supervisor: 141 - Agostinho Gomes

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

This thesis proposal focus on the development, implementation and integration of a high voltage (HV) system to be used in the Tilecal calorimeter for the operation in the future High Luminosity LHC (HL-LHC) environment (upgrade Phase II). Tilecal, the ATLAS hadron calorimeter in the barrel region is a key sub-detector used for the measurement of jets energy, missing transverse energy, identification of muons with low transverse momentum and for other physics' tasks. All the Tilecal electronics is being upgraded for the HL-LHC operation. The current HV system is based on a HV distributor system located in the detector that receives a single HV per module as input and regulates the individual voltages to be applied locally to each photomultiplier tube (PMT). This concept has been in use in the Tilecal, and it has the important advantage of not requiring (a large number of) 100-150 m long cables from the HV regulator to the PMTs. In the upgrade, the HV system will be replaced since it has two drawbacks: the radiation damage and the impossibility of replacement of boards if a problem occurs since access is difficult and is possible only at the LHC shutdowns. The new HV system for the upgrade Phase II is a remote one. The HV boards will fit in crates that provide low voltage and that are located outside the ATLAS main cavern. They use standard electronics components since they are not located in the areas exposed to radiation inside the detector but this solution has the drawback of requiring a large number of long cables. A new control and monitoring system is being developed. The HV regulation and the respective control system designs are being finalized and the prototypes will be tested in the calorimeter environment in setups similar to the one of the ATLAS detector, using beams of high energy pions, electrons and muons at CERN and likely also in a special module that will operate in the ATLAS detector. These tests will allow to access the performance of the new Tilecal electronics that is being developed for the HL-LHC. Linearity, stability and noise of the developed system will be measured in the tests with beams of high energy particles and whenever possible in the ATLAS detector during the LHC Run 3 that will start in 2021. A special prototype called demonstrator featuring the new electronics for Phase II will be produced and it is expected to be inserted in the ATLAS detector for regular operation during LHC operation in Run3. This full integration in ATLAS will allow to test the system in the normal conditions of operation before the Phase II upgrade takes place and will give useful information about the performance for the future operation in Phase II.

10B-RPCs: An innovative concept for neutron imaging detectors

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1712 - Luís Margato

Co-Supervisor: 1719 - Andrey Morozov

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

Neutron detectors are powerful tool finding application in a wide range of scientific disciplines including material sciences, condensed matter physics, chemistry, and health, life and heritage sciences among many others. Integrated in sophisticated instruments at large scale neutron facilities (e.g. ILL, ISIS, FRM II and ESS) neutron detectors are fundamental for revealing the structure and function of matter from the microscopic down to the atomic scale, using neutrons as a probe. Until recently, these detectors were mainly based on the 3He isotope, the gold standard in thermal neutron detection. However, the construction of new high intensity spallation neutron sources, most importantly the European Spallation Source (ESS), coinciding with the world-wide drastic shortage of 3He, are driving a growing need for a new generation of neutron detectors. In response to this challenge a significant effort is made to develop new detection technologies. However, the state-of-the-art detectors based on 3He alternatives cannot yet offer a combination of performance characteristics achieved with 3He detectors, while modern scientific and industrial applications set even more demanding requirements. This thesis proposal aims to develop an innovative neutron detector technology which combines Resistive Plate Chambers (RPC) and solid-state neutron converters containing 10B isotope (10B-RPCs). This technology has a great potential for neutron imaging applications due to an unprecedented combination of very high temporal and spatial resolutions. It also offers excellent scalability at low cost, making 10B-RPCs attractive for building large area detectors, and particularly well suited for applications requiring neutron imaging detectors which can provide accurate neutron time of flight (TOF) information. Access to the TOF is of the utmost importance to exploit the pulsed nature of spallation sources (such as, e.g., ISIS Neutron and Muon Source at the UK and the European Spallation Source currently under construction in Sweden). One of the main goals is to reach spatial resolutions of 0.1 mm FWHM. The plan involves performing detailed Monte Carlo simulation studies, exploiting very narrow gas gaps (<0.35 mm), and developing new position reconstruction algorithms based on statistical methods and machine learning techniques. Another major goal is to demonstrate a high counting rate capability (>100 kHz/cm²). Three approaches will be followed: 1) use of new materials with low electrical resistivity; 2) exploit the dependence of the resistivity of materials on temperature; 3) Find the most favourable multilayer RPC geometry for high count rate operation (count rate scales nearly linearly with the number of layers) and strong gamma ray discrimination. The third goal is twofold: firstly, to design and built an RPC-based neutron detector prototype with both high spatial resolution (~0.1 mm) and high counting rate capability (>100 kHz/cm²) satisfying the requirements of applications in Neutron Scattering Sciences; secondly, to explore a possible application of RPC-based neutron detectors for the measurement of beta delayed neutron emission probability from very exotic neutron-rich nuclei in ISOLDE at CERN. This probability directly affects the final abundance distribution of the elements in nucleosynthesis processes like the r-process, responsible for the production of half of the elements in the universe and offer the possibility of contributing to the understanding of how heavy nuclei are produced in neutron star collisions. Currently, these measurements are normally performed using 3He-counters, which due to the shortage and prohibitive price of 3He cannot be implemented in the required areas. It is expected that this innovative detection technology will find immediate applications at large scale neutron facilities. Another direct application is expected in homeland security. The possible areas of technology spillover include industrial neutron tomography, which is a complementary technique for X-ray tomography; real-time imaging of blending and chemical reactions in the chemical industry; and analysis of the structure and flow of biphasic fluids in the oil industry. The thesis proposal is to be developed by a synergistic collaboration of LIP and the ESS detector coatings group, with a strong involvement of detector groups from the world-leading neutron facilities in Europe: ISIS, ILL and FRMII.

Neutrino and Dark Relics of Grand Unification

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1693 - António Morais

Co-Supervisor: 1713 - Felipe Ferreira de Freitas

Co-Supervisor: 1723 - Roman Pasechnik

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: Mixed

Abroad-Institution: THEP Group - Lund University, Sweden

The last decade witnessed the confirmation of three outstanding milestones in fundamental physics recognized with the attribution of three Noble Prizes. In 2013, such an award was granted to the Higgs boson discovery dated from 2012 thus completing the Standard Model (SM) of Particle Physics. 2017 was the year of conceding the Nobel Prize to the discovery of Gravitational Waves in 2015, 100 years after Einstein has published his theory of General Relativity. Last but not least, 2015 was also the year where the discovery of neutrino flavour oscillations in 2002 was rewarded with a Nobel Prize. The latter discovery is one of the strongest evidences that the SM is by no means a complete description of particles and interactions. In fact, flavour oscillations between different neutrino species imply a quantum superposition of mass eigenstates which the SM cannot offer. Furthermore, the existence of dark matter (DM), from galaxy rotation curves and anisotropies in the Cosmic Microwave Background is becoming increasingly favoured by a particle physics explanation that is absent in the SM. This follows from recent observations of the bullet cluster that show a dramatic offset between the visible plasma and the gravitational potential inferred from lensing, disfavouring, for instance, a modified gravity solution. With this thesis we aim at exploring both the DM and neutrino mass problems in a well defined and particularly attractive New Physics framework based on a trinification Grand Unified Theory (T-GUT) supplemented by a gauge family symmetry. Besides the unification of forces, this high-scale theory also features the unification of the Higgs and matter sectors. Therefore, the existence of a large unified representation yields a rich neutrino sector at the low-scale containing 9 Dirac weakly interacting components, of which 3 are sub-eV, and 6 heavy Majorana ones. One of the key studies proposed to develop in this thesis is to understand which regions of the parameter space allow for a Pontecorvo–Maki–Nakagawa–Sakata (PMNS) mixing and which implications it poses to the high-scale theory. Furthermore, the lightest Majorana neutrino can be sterile enough to provide a good candidate for the DM. Finally, the new Dirac-type heavy neutrinos are accompanied by three generations of vector-like leptons offering an interesting opportunity for collider searches and phenomenological studies at the Large Hadron Collider. These studies involve the development of algorithms based on probabilistic programming language and Bayesian Deep Learning. Such techniques will be used as a generative model environment, allowing us o make a Monte-Carlo event generator, such as MadGraph or Pythia, to work in a more efficient way by looking for model parameter space points consistent with both theory and experimental data.

Heavy Flavour Jets Production in Heavy Ion Collisions at the High Luminosity LHC with the ATLAS Detector

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 92 - Helena Santos

Co-Supervisor: 55 - Patricia Conde Muino

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Context: Ultrarelativistic nucleus-nucleus collisions at the Large Hadron Collider (LHC) provide an unique opportunity to recreate the Quark Gluon Plasma (QGP) in the laboratory energy frontier. This plasma of quarks and gluons, which is known to behave as a nearly perfect liquid, was the prevailing state of the Universe shortly after the Big Bang. The capabilities of ATLAS, namely large acceptance and high granularity calorimeters, afford excellent handles for QGP studies. The ATLAS experiment is strongly committed with the HI program of LHC and great expectations on the capabilities of the Upgrade to bring deeply understanding on the nature of the QGP are raised. A major goal of the Heavy Ion Program of the LHC is the understanding of the effects of the QGP on jets, namely the study of the nature of the energy loss suffered by the quarks and gluons while crossing the QGP. The bottom quark, in particular, constitutes an excellent probe. Due to its large virtuality, Q, it has a formation time,∆t ≈1/Q ≈ 0.1 fm/c, much smaller than the formation time of the QGP at the LHC (≈10 fm/c). The understanding of the nature of the energy loss (either collisional or gluon radiative), by its turn, is crucial to infer the properties of the QGP. The HI ATLAS/LIP group is contributing with important developments preceding the b-jet physics analysis, namely on b-jet reconstruction, b- tagging and b-jet triggers in HI collisions. Objectives: The goal of the proposed thesis is the prospective study of the Heavy Flavour jets production in the HL-LHC phase (expected to start in 2027) benefiting from the 1 order of magnitude increased luminosity foreseen for the Pb+Pb runs. The most important ATLAS upgraded components for the proposed project are the calorimeters front-end electronics and the new tracker detector. Currently jets are reconstructed using the transverse energy of calorimeter towers (piled cells) as input signals, after subtracting the QCD underlying event. The new readout electronics of the calorimeters will provide support for a more sophisticated detector signal processing. The remaining part of jet reconstruction regards the identification of the b-jets, i.e. b-tagging. This technique aims the highest possible efficiency for tagging b-jets, with the largest possible rejection of light jets. In ATLAS the most used techniques take advantage of the relatively long lifetime of hadrons containing bottom quarks (ctau 450 mm), as well as of the hard fragmentation and the high mass of these hadrons. These properties lead to tracks in the ITk with large impact parameters (i.e., transverse and longitudinal distances of closest approach of the track to the primary and secondary vertices), on contrary to the tracks from light jets. Such a feature allows to disentangle heavy flavour jets from light jets, but it requires excellent impact parameter resolution. This is ensured by the ITk. Machine learning techniques using the properties of both the impact parameters and the secondary vertices have proven to increase significantly the b-tagging performance in pp collisions and the development in Pb+Pb is ongoing. Analysis of data taken in Run 2 and Run 3 of LHC will provide not only results on Heavy Flavour jets in HI collisions per se, but will also contribute preciously to the validation of the prospective study in the HL-LHC. Requirements: This is an experimental PhD program. The work will be developed at LIP - Laboratorio de Instrumentacao e Fisica Experimental de Particulas. The student should have solid computing skills, namely in C++ programming. Furthermore, she/he will concurrently participate in the technical activities in which the ATLAS/LIP group is involved, namely in the Tile calorimeter and/or in Trigger systems.

Ultra-light bosons, compact objects and gravitational waves

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1476 - Carlos Herdeiro

Co-Supervisor: 1693 - António Morais

Co-Supervisor: 1477 - Nicolas Sanchis-Gual

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: National

Ultra-light bosons are, at the moment, one of the competing candidates for explaining dark matter. Such particles can gravitationally collapse to form dark matter stars, called bosonic stars, and interact non-trivially with black holes, forming halos around them. The goal of this thesis is two fold. First, to obtain the gravitational wave phenomenology from bosonic stars and black holes with bosonic halos, comparing and contrasting it with that of canonical black holes or neutron stars. This is of interest to the ongoing LIGO-Virgo science runs and uses numerical relativity techniques. Secondly, to investigate the viability of particle physics models that can accommodate such ultralight bosons with focus on U(1) extensions of the standard model.

Black hole shadows, the Kerr hypothesis and fundamental physics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1476 - Carlos Herdeiro

Co-Supervisor: 1730 - Pedro Cunha

Host Institution: CIDMA - Centro de Investigação em Matemática e Aplicações da Universidade de Aveiro

Degree Institution: Universidade de Aveiro

PhD Program:

Typology: National

The Event Horizon Telescope produced in 2019 the first image of a black hole resolving horizon scale structure. Imaging the strong gravity region around such compact objects probes can test the Kerr hypothesis. That is the hypothesis that astrophysical black holes are well described by the Kerr metric. In the last few years, new black hole solutions and horizonless compact objects have been proposed if novel very light bosonic particles exist, that are dark matter candidates. The goal of this project is to study the strong gravitational lensing by this non-Kerr compact objects, using ray tracing codes and General Relativistic Magneto-Hydrodynamic simulations, to obtain images that can be compared with the EHT data. This will constraint models of ultralight scalar fields and possibly shed new light on the nature of dark matter.

2 Fast 2 Furious Universe

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1497 - Tiago Barreiro

Co-Supervisor: 633 - Nelson Nunes

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The realization that the Universe is accelerating propels the need for a dark energy component with negative pressure. This project aims to understand the nature of dark energy and how it interacts with the other particles: dark matter, neutrinos, baryons and photons. The student will construct and investigate the theoretical aspects of a class of scalar tensor theories and will evaluate its viability by testing it against current and forthcoming observational data (ESPRESSO, Euclid, Lisa). This is both a theoretical and hands on data project.

Heavy Flavour Jets Production in Heavy Ion Collisions in Run 3 of the LHC with the ATLAS Detector

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 92 - Helena Santos

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Context: Ultrarelativistic nucleus-nucleus collisions at the Large Hadron Collider (LHC) provide an unique opportunity to recreate the Quark Gluon Plasma (QGP) in the laboratory energy frontier. This plasma of quarks and gluons, which is known to behave as a nearly perfect liquid, was the prevailing state of the Universe shortly after the Big Bang. The capabilities of ATLAS, namely large acceptance and high granularity calorimeters, afford excellent handles for QGP studies. A major goal of the Heavy Ion Program of the LHC is the understanding of the effects of the QGP on jets, namely the study of the nature of the energy loss suffered by the quarks and gluons while crossing the QGP. The bottom quark, in particular, constitutes an excellent probe. Due to its large virtuality, Q, it has a formation time,∆t ≈1/Q ≈ 0.1 fm/c, much smaller than the formation time of the QGP at the LHC (≈10 fm/c). The understanding of the nature of the energy loss (either collisional or gluon radiative), by its turn, is crucial to infer the properties of the QGP. The HI ATLAS/LIP group is contributing with important developments preceding the b-jet physics analysis, namely on b-jet reconstruction, b-tagging and b-jet triggers in HI collisions. Objectives: The student will participate in Pb+Pb data acquisition at CERN already during Run 3 (expected for the Falls of 2021-22-23-24) and will analyse the data. The analysis will explore strategies, namely machine learning techniques, to separate the b-quarks jets from light jets (mostly u- and d-quarks) and further separation of b-quarks jets originating directly from the hard process from those arising from gluon splitting with the aim of devising novel experimental observables sensitive to the different energy loss of quarks and gluons. Requirements: This is an experimental PhD program. The work will be developed at LIP - Laboratorio de Instrumentacao e Fisica Experimental de Particulas. The student should have solid computing skills, namely in C++ programming. Furthermore, she/he will concurrently participate in the technical activities in which the ATLAS/LIP group is involved, namely in the Tile calorimeter and/or in Trigger systems.

Busca de processos raros no LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

A descoberta do bosão de Higgs em 2012 tornou o modelo padrão das partículas elementares completo. Contudo, a busca de novas partículas ainda não terminou: vários fenómenos observacionais bem estabelecidos - massas e oscilações de neutrinos, matéria negra, assimetria entre matéria e anti-matéria no universo observável - não podem ser explicados apenas com partículas conhecidas. Não terem sido encontrados até agora sinais definitivos de novas partículas sugere que estas possam ter massas demasiado elevadas para poderem ser diretamente produzidas no LHC, ou que tem acoplamentos muito debeis com as partículas do modelo padrão -- resultando assim em processos raros. A busca de processos raros, que são fortemente suprimidos no modelo padrão, é um modo privilegiado e especialmente promissor para detectar nova física. A fase de alta luminosidade do LHC que agora se inicia fornece sensibilidade para a detecção de processos ultra-raros, e sensíveis a partículas novas com massas muito superiores à energia de colisão do LHC. A observação do decaimento Bs→μμ por CMS e LHCb [Nature, 522 (2015) 68] é considerada a decoberta mais emblemática do LHC a seguir à descoberta do bosão de Higgs, e que impôs restrições consideráveis em modelos de supersimetria, entre outros. Esta descoberta, co-liderada por investigadores do LIP, demonstra bem a capacidade do detector CMS no que respeita a buscas e medidas de processos raros. O próximo grande passo será a descoberta do decaimento ainda mais raro: B0→μμ. Este projeto de Tese consiste na participação nesta importante análise do LHC, com os dados acumulados durante o mais recente período de tomada de dados (Run2) bem como a preparação do seguinte período (Run3). Existe ainda a possibilidade de explorar outros decaimentos raros de alta sensibilidade a física nova (envolvendo para além do B as partículas tau, Z e Higgs). A investigação será desenvolvida no contexto da participação Portuguesa na experiência CMS do LHC; da avaliação dos grupos de investigação levada a cabo por painel internacional nomeado pela FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”.

Cosmological tests of gravity theory beyond General Relativity

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 466 - Francisco Lobo

Co-Supervisor: 1500 - Noemi Frusciante

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

An outstanding problem faced by modern cosmology concerns cosmic acceleration, i.e. the phase of accelerated expansion recently entered by the Universe, for which we still lack a satisfactory theoretical explanation. Within the context of General Relativity, an accelerated expansion can be achieved adding an extra ingredient in the energy budget of the Universe, commonly referred to as dark energy. A different approach is to modify the law of gravity describing the Universe at large scales. A plethora of modified gravity models addressing the phenomenon of cosmic acceleration have been proposed and analyzed. The astronomical community has embarked on an intense observational effort to help exploring the real nature of the cosmic acceleration. Up and coming missions will deliver highly accurate data, offering an unprecedented insight into gravity on cosmological scales. This observational effort is not yet balanced by an equally focused effort at theoretical modeling. The ability to constrain various properties of cosmological models using observational data, such as the anisotropies of the cosmic microwave background, the large scale structure of the galaxy distribution, the expansion and acceleration rate of the universe and other such quantities, has become an essential part of modern cosmology. The goal of the PhD project will be to unveil the real nature of the theory of gravity. To achieve this, the student will apply theoretical modeling and numerical methods to the best data available and perform forecasts for future next generation surveys. Development of this project is required for several reasons 1) new theoretical models need to be built; 2) new numerical patches need to be developed which serve to test models against cosmological observations. The analysis tools developed by the student are expected to be used in the upcoming ESA Euclid mission in which the host institution has a leading role. In order to ensure a successful PhD, this project contains theoretical and numerical elements that are flexible such that they can fit with the student’s skills and expertise.

Testing the Early Universe with Gravitational Waves

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 111 - José Pedro Mimoso

Co-Supervisor: 633 - Nelson Nunes

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The remarkable detection of Gravitational Waves by LIGO has opened a new window for the scrutiny of physical phenomena in the Universe. In particular, as soon as the precision of the detectors reaches the level which enables detection of the stochastic background of gravitational waves, it will become possible to probe the Universe prior to the recombination era, only 400 000 years after the Big Bang. Possibly, it will even enable us to gather direct information of processes taking place at the very Early Universe when energies approach the Planck scale and all the fundamental forces, including gravity, are expected to be symbiotically unified. In this PhD project we aim to use of the information carried by the stochastic background of gravitational waves to test crucial high energy physics stages such as the electroweak phase transition and the epoch of reheating that followed the period of inflation. This work seeks, therefore, to shed light on the mechanism that bridges the process of inflation that gives us the flat Universe and its large scale structure and, the production of fields that make up the Standard Model of particle physics.

Coding the Cosmos: Simulating Superstrings in the GPU Era

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 184 - Carlos Martins

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

Cosmic strings arise naturally in many proposed theories of new physics beyond the standard model unifying the electroweak and strong interactions, as well as in many superstring inspired inflation models. In the latter case, fundamental superstrings produced in the very early universe may have stretched to macroscopic scales, in which case they are known as cosmic superstrings. If observed, these objects thus provide a unique window into the early universe and possibly string theory. Recent progress in CMB polarization and gravitational wave detection highlights how some of these scenarios can be constrained by high-resolution data. However, they also show that the current bottleneck is the lack of accurate high-resolution simulations of defect networks that can be used as templates for robust statistical analysis. This will be an even bigger problem for next-generation facilities such as CORE and LISA. This thesis will continue the recently started deployment of a new generation of high-scalability GPU-accelerated defect codes that will match the sensitivity of ongoing and forthcoming observational searches.

Charmonium hadroproduction studies: a machine learning approach

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 471 - Catarina Quintans

Co-Supervisor: 64 - Pedro Abreu

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The formation mechanism of hidden charm resonances, the so-called charmonium states, is governed by the theory of strong interactions, Quantum Chromodynamics. Essential aspects of the theory remain poorly known and require new experimental inputs for which the analyses are very challenging. The spin-dependent behavior of these resonances and the connection to different production mechanisms is one of the main physics topics addressed in hadron-induced fixed-target experiments done at intermediate energies. The COMPASS experiment at CERN recently collected a very large data sample, optimally suited for such studies. The proposed PhD topic consists in the analysis of these data using innovative machine learning and deep neural network methods. The potential of such techniques in separating prompt and feed-down contributions and distinguishing the charmonium signal from physics backgrounds will be explored. The new AMBER project at CERN represents a step forward in charmonium studies at the intermediate energies regime. The open spectrometer configuration being planned brings entirely new prospects for clean and direct detection of different charmonium states. The studies proposed will be very important to define the charmonium physics accessible at AMBER, and find the optimal experimental conditions that maximize the significance of observables.

Search for dark matter at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 144 - Joao Varela

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The subject of this thesis is the search for New Physics in events with jets, with W or a Z boson produced in association with large missing transverse energy. Dark matter (DM) is one of the most compelling pieces of evidence for physics beyond the standard model (SM). In many theories, pair production of DM particles in hadron collisions proceeds through a boson mediator of either spin-0 or spin-1. DM particles can be produced in pairs association jets or with a vector boson V (where V is either a W or a Z boson) and recoil with large missing transverse energy. This results in the `MET+X’ final state. The thesis is placed in the context of the Portuguese participation in the CMS experiment at the LHC, and it is linked to the Beyond the Standard Model (BSM) searches in the more general context of the searches for New Physics processes at the LHC. The candidate is expected to work in a team with a group of researchers.

Top quark physics and searches for New Physics at the Large Hadron Collider

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 144 - Joao Varela

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Top quarks are abundantly produced in pairs at a hadron collider, and they constitute the main background to searches for New Physics. In the framework of the Standard Model (SM), each top quark decays into a W and a b quark. A good understanding of the top quark events will allow a more sensitive reach into the realm of searches for Beyond SM (BSM) processes. Recent checks of lepton flavour universality violation sparked a renewed interest towards measurements involving tau leptons, owing to a potential disagreement with SM predictions. The work will focus on studying the properties of the top quark dilepton final state and measure the tau and heavy flavour contents of top quark events. Studies of final states, including 3rd generation leptons and quarks such as tau leptons and b-jets, produced in association with top quark pair events may provide first hints for New Physics processes and shed light on the anomalies of Lepton Flavor Universality measurements. An anomalous flavor production is directly “visible” in this study. Deviations from SM predictions will indicate evidence for New Physics. The research will be carried out in the context of the Portuguese participation in the CMS experiment at the LHC, in the framework of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”. The candidate is expected to work in a team with a group of researchers.

Search for New Physics in exclusive processes at the LHC

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 129 - Michele Gallinaro

Co-Supervisor: 802 - Jonathan Hollar

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Production of exclusive processes occurs with high cross section in gamma-mediated processes at the LHC. Photon-photon collisions may provide the conditions to study particle production with masses at the electroweak scale. By tagging the leading proton from the hard interaction, the Precision Proton Spectrometer (PPS) provides an increased sensitivity to selecting exclusive processes. PPS is a detector system to add tracking and timing information at approximately 210 m from the interaction point around the CMS detector. It is designed to operate at high luminosity with up to 50 interactions per 25 ns bunch crossing to perform measurements of e.g. the quartic gauge couplings and search for rare exclusive processes. Since 2016, PPS has been taking data in normal high-luminosity proton-proton LHC collisions. The goal of the internship is to select and identify for the first time in data the extremely rare processes of heavy particles – including top quarks and W bosons - produced exclusively and identified with proton tagging. The research will be carried out in the context of the Portuguese participation in the CMS experiment at the LHC in the more general context of the searches for New Physics processes at the LHC, in the framework of the activities of one of the outstanding research groups in High-Energy Physics in Portugal. Citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”. The candidate is expected to work in a team with a group of researchers.

Expecting the unexpected: going beyond the standard searches for vector-like quarks at the ATLAS experiment at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 26 - Nuno Castro

Co-Supervisor: 341 - Miguel Crispim Romão

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program:

Typology: National

A cornerstone of the Standard Model (SM) of Particle Physics is the formulation of the electroweak interactions as arising from a spontaneously broken gauge symmetry. Experiments over the past four decades have confirmed this hypothesis with precision, most notably the LEP and SLC collider programs. The ATLAS and CMS collaborations reported in 2012 observations of a new particle produced at the CERN Large Hadron Collider (LHC) possessing properties so far consistent with those predicted for the SM Higgs boson. It should be noted, nonetheless, that the exact nature of the symmetry-breaking mechanism is not yet determined. Furthermore, regardless of the many experimental validations of the SM, it is known that it cannot be regarded as a final theory, given the many problems it fails to solve, namely the hierarchy problem, the lack of a dark matter candidate, matter-antimatter asymmetry, and others. Attempting to solve these problems, many beyond the SM theories were built. Vector-like quarks (VLQ) are featured in some of these models, as spin 1/2 fermions, color triplets with the same left and right quantum numbers, mixing with SM quarks. Both the ATLAS and CMS experiments have developed a comprehensive search program for vector-like quarks. Nonetheless, and despite a significant effort to present general results, most of these analysis made important assumptions on the production and decay modes of the vector-like quarks and thus missing possible alternative signatures, which can have strong phenomenological motivations. The current proposal foresees the development and implementation of a search for vector-like quarks which can be produced in pairs via a heavy gluon or decay into new scalars. Given the multitude of final states that vector-like quark production can have, the search strategy will rely on the use of deep learning. A complete experimental analysis, considering a detailed study of the modelling of backgrounds and sources of uncertainties will be developed. The phenomenological consequences of the experimental results will be also be studied, in close collaboration with the Phenomenology group at LIP. The current proposal will be integrated in the Portuguese ATLAS team and collaboration with several international groups is foreseen.

Scintillating array for real-time high-resolution ion therapy dosimetry

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1718 - Jorge Sampaio

Co-Supervisor: 342 - Luis Peralta

Co-Supervisor: 73 - João Gentil Saraiva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Radiobiological effects depend strongly on the track-structure of particles crossing the tissues. The clustering of energy deposition determines the degree of cell damage and the ability of cells to repair. Thus, an important component of radiobiology experiments is the measurement of doses with high spatial resolution and as close as possible to the irradiation conditions of the irradiated tissues. The objective of the project is to develop a detector prototype that combines tissue-equivalence, the unique capability to support cell growth, real-time dose measurements with high spatial resolution, and cost-effectiveness. The detector will be constructed of juxtaposed thin plastic scintillating fibers coupled with a system for reading and converting the optical signal into deposited energy. The project involves tasks of design and construction of the detector and associated electronics, simulations of the detector's response to proton and heavy-ion radiation fields, tests, and calibrations of the detector with radioactive sources and particle beams. The Ph.D. student will be integrated into a team with extensive experience in the development of detectors based on scintillating fibers and in Monte Carlo simulations. The work will be carried out in national and international collaborations with biology research laboratories and particle accelerator facilities.

Probing the Electroweak Vacum with di-Higgs production at the ATLAS experimente at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 484 - Ricardo Gonçalo

Co-Supervisor: 1715 - Konstantinos Nikolopoulos

Co-Supervisor: 140 - Filipe Veloso

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: Mixed

Abroad-Institution: University of Birmingham

Since its discovery, the Higgs boson became a prime tool to search for physics beyond the Standard Model (SM). At the current level of precision, the Higgs boson is compatible with SM expectations. A number of open questions suggest the existence of new physics, that could be unveiled as we explore the LHC data. A wealth of experimental results from the ATLAS and CMS experiments, probe the region around the minimum of the Higgs potential, or vacuum. But the shape of this potential is not constrained experimentally. This shape is intimately connected to the breaking of the electroweak gauge symmetry, which resulted in the fundamental forces we experience today. To experimentally constrain this shape we must measure the Higgs boson self-coupling, which is accessible at the LHC through the simultaneous production of two Higgs bosons. The selected student will join the Portuguese ATLAS team, working in close collaboration with theorists and integrated into our international collaboration. He or she will be able to contribute to enhancing our current knowledge in this important area, which will become one of the most important measurements of LHC experiments. The student will also employ the latest theory developments and the most recent advances in reconstruction techniques: from boosted object identification to machine learning. Part of this research will be done at the University of Birmingham, in the United Kingdom, in co-supervision with a colleague from the ATLAS collaboration. The successful student will be able to participate in the operation of the ATLAS experiment during the LHC Run 3 to start in 2021, and travel to CERN will be required.

Characterization of liquid argon detectors for next generation neutrino physics

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 32 - José Maneira

Co-Supervisor: 69 - Fernando Barao

Co-Supervisor: 1729 - Francesco Pietropaolo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: Mixed

Abroad-Institution: CERN

The technology of liquid argon time projection chambers (TPCs) allows for massive detectors with excellent tracking and calorimetry -- all crucial capabilities to meet the requirements of the next generation long baseline neutrino experiments. In this technique, electrons drift in an intense electric field and are collected in wire anodes planes, with the measured time providing the drift length. A full characterization of the electric field uniformity and the charge attenuation along the drift are essential to guarantee a precise 3D reconstruction of the neutrino interaction and its energy. This project will be based on the development of calibration and characterization techniques of LAr TPCs with cosmic ray muons, intense UV laser beams, and possibly a dedicated radiation source. It will be focused on the DUNE experiment and its prototype at CERN, ProtoDUNE. New calibration systems will be installed in ProtoDUNE in 2021, with the aim of taking data from 2022 onwards. The commissioning, calibration and data analysis of ProtoDUNE2 will be the central part of this work plan, that will conclude with using those results to better estimate the performance of the future DUNE far detector. The candidate will integrate the CERN Neutrino Platform team and will play an active role in the ProtoDUNE Phase II installation. He/she could take responsibility of the commissioning and, possibly, on early operation for a specific device of the calibration apparatus.

Measurement of the pion and kaon structures by COMPASS and AMBER experiments at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 164 - Márcia Quaresma

Co-Supervisor: 1718 - Jorge Sampaio

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The structure of the hadrons, in particular the pion and kaon mesons, can be directly addressed by the measurement of the pion/kaon induced Drell-Yan process. These measurements give access to the structure of the pion/kaon in terms of the valence and the sea quarks, and how much they contribute for the pion/kaon properties, such as their masses. This contributes for a better understanding of the Quantum Chromodynamics mechanisms governing the origin of the mass of the non-elementary particles. COMPASS is a fixed target experiment at CERN, where data on Drell-Yan with negative pion beam were collected in 2015 and 2018. These data just started to be analysed. One of the goals is to extract the pion valence distribution. AMBER is a new experiment being proposed at CERN which aims to further study the pion and also the kaon structures, among other physics topics. In this thesis the student will analyse the COMPASS data and perform simulations and developments for the new AMBER measurements. The available COMPASS data will profit the implementation of the new experiment and boost its potential. Part of the work is the optimization of the spectrometer design to cope high intensities while keeping the detectors performance and the radiation under control.

A deeper look in the cosmic Large-Scale Structure

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1734 - Giuseppe Fanizza

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Recent progresses in numerical relativity are providing interesting non-gaussian features in the statistical properties of inhomogeneities on large scales. These features are significant at the same level of precision achievable by forthcoming observations for both LSS surveys and CMB. The aim of this thesis is to investigate the analytical behavior of the non-gaussianities, in order to understand if and at which level cosmological higher-order perturbation theory descriptions breaks down and to which extent future observations will be able to discriminate among alternative scenarios to Cosmological Concordance model and different dark matter candidates.

Harnessing the Power of Deep Learning for New Physics Searches at Colliders

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 341 - Miguel Crispim Romão

Co-Supervisor: 26 - Nuno Castro

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade do Minho

PhD Program:

Typology: National

When searching for New Physics (NP) at the collider data, Machine Learning (ML) can provide enhanced sensitivity through highly performant supervised discriminants that separate signal from background, such as Gradient Boosted Trees (GBT). With the advent of Deep Learning (DL) and its groundbreaking impact in ML, there has been a lot of interest in studying the potential of DL for NP searches in order to further improve NP sensitivity. In this thesis we will explore the potential of DL at NP searches. We will systematically study how they compare to GBT and similar traditional ML methods, as well as understand in which context DL can surpass them in performance. Of particular interest, we will develop appropriate methodologies to use high-level physical observables from reconstructed objects at colliders, and implement methods to guarantee interpretability of the models to further the physics understanding of phenomena at colliders. Another avenue that will be explored in this thesis is how we can use DL to develop generic searches for NP, such that we do not commit to an explicit hypothesis of NP phenomenon and realisation. This task is especially crucial, as with the High-Luminosity LHC upgrade we expect the data intake to increase tenfold, which therefore requires extra efforts to to guarantee that we are not missing out on any NP present in the data.

Effect of dark matter on the nuclear and quark superfluidity inside the compact stars

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 17 - Ilidio Lopes

Co-Supervisor: 1474 - Violetta Sagun

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Accumulation of dark matter (DM) inside the neutron stars (NSs) may significantly change the thermodynamic properties of the stellar matter. Moreover, it may effect the cooling of the compact stars by modifying the neutrino and photon emission processes. Thus, the neutrino emission is strongly dependent on the occurrence of pairing between the particles, since an existence of a gap in the single particle excitation spectrum leads to its suppression. The existing astrophysical data on cooling of compact stars provide us with a possibility to constrain their internal composition, the nucleon pairing gaps and modifications due to the presence of DM. The first part of the project will be focused on the impact of DM on the nuclear superfluidity/superconductivity in the interior of NSs. The second part will be dedicated to the effect of DM on the quark superfluidity in the core of the hybrid stars (HSs) that may contain a quark-gluon plasma. The project includes the development of the theoretical model, as well as working with the thermal evolution code for the compact stars. The candidate is required to have a strong background in QCD and related topics. Its a joint PhD fellowship between the University of Lisbon, a group of Prof. Ilı́dio Lopes, and Dr. Violetta Sagun at the University of Coimbra.

Search for nucleon decay in large liquid argon experiments

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1487 - Nuno Barros

Co-Supervisor: 32 - José Maneira

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Proton decay, and the decay of nucleons in general, constitutes one of the most sensitive probes of high-scale physics beyond the Standard Model. The most sensitive experiments up until now are mostly based on water-cherenkov signal detection, which are primarily sensitive to decay channels involving pions. The DUNE experiment is a next-generation long-baseline neutrino experiment that will use liquid argon time projection chamber (LAr-TPC) technology to detect the physics events. By using LAr, DUNE is particularly sensitive to decay channels involving kaons, adding a new set of channels to explore. The goal of this project is to pursue the search of nucleon decay modes through the Kaon decay channels. During the first run of the ProtoDUNE prototype at CERN, a specific trigger signal was put in place to identify kaons produced from the test beam. This allowed to obtain a pure sample of kaon events in the ProtoDUNE-I dataset, that can now be used to implement advanced algorithms to identify and reconstruct not only the Kaons, but also the products of their decay. This project will initially use the ProtoDUNE-I dataset to implement algorithms that will later be applied to the dataset of the second run of ProtoDUNE and used to estimate the sensitivity of the full DUNE experiment.

Probing particle physics with gravitational waves

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 478 - Lara Sousa

Co-Supervisor: 167 - Pedro Avelino

Host Institution: Centro de Astrofísica da Universidade do Porto

Degree Institution: Universidade do Porto

PhD Program:

Typology: National

The detection of gravitational waves by the LIGO interferometer precipitated us into a new era of astronomy: the era of Gravitational Wave Astronomy. Gravitational waves will allow for the detection of new astronomical sources, enabling us to hear what is currently unseen. In this doctoral project, we will develop a new generation of numerical algorithms to describe cosmic defect networks, with the objective of gaining new understanding of their evolution and of constructing more realistic semi-analytical descriptions of their dynamics. These tools will enable us to study the gravitational wave background and other observational signatures generated by cosmic defect networks (including cosmic superstrings) with unprecedented precision. The production of these defects in symmetry breaking phase transitions in the early universe is predicted in several models of particle physics. This work will then give us insight, not only about the physics of the early universe, but also about fundamental physics. Stringent constraints on defect-forming scenarios will also be derived using upcoming gravitational wave data (e.g. from LIGO-VIRGO,IPTA,LEAP), in order to discriminate between different models of particle physics at extremely high energies. Detailed forecasts for upcoming probes, such as LISA (of which the both supervisors are members) and SKA, will be central to this project too.

Parton showers for the next generation of jet quenching studies

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 107 - José Guilherme Milhano

Co-Supervisor: 30 - Liliana Apolinário

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Quark-Gluon Plasma (QGP) produced in ultra-relativistic collisions is a remarkable manifestation of emergent complexity. QGP’s nearly perfect liquid behaviour arises from simple fundamental interactions between elementary degrees of freedom of Nature: quarks and gluons. In heavy-ion collisions, jets - a spray of collimated particles originated by a quark or gluon - are produced concurrently with the QGP. These objects already proved to be an invaluable probe to measure the QGP’s dynamical properties. The upcoming high-luminosity phase of the LHC will provide an order of magnitude increase on the available data leading to extremely precise measurements and the possibility to explore a range of different nuclei with the aim of identifying the minimal size and density conditions compatible with the creation of a QGP. Suitably precise theoretical descriptions must match this future experimental high precision. Parton showers, the procedure through which multiple QCD branching leading to jets is simulated, and from which jet properties can be computed systematically, are a cornerstone of the current theory effort. Up to now, parton showers used for calculation of jets modified by their interaction with the QGP (jet quenching) have been adapted from those formulated when no QGP is present (e.g., in proton-proton collisions). The aim of this thesis is to formulate a new parton shower strategy uniquely suited for QGP studies where jet and QGP evolutions can be described in a common ordering variable. The work will involve the analytical formulation of the parton shower and its computational implementation.

Seeds for the Next Frontier Detectors: Lessons from the TileCal/ATLAS Operation and R&D on Emergent Scintillating Materials

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 1717 - Rute Pedro

Co-Supervisor: 74 - Amelia Maio

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Currently, the field of Particle Physics is planning the next generation experiments with options for CERN-based accelerators, namely the FCC cicular collider, under consideration by the update of the European Strategy for collider HEP. *On the other hand*, the main technological challenges in the R&D for the future detectors are already identified and are input for the decision. Calorimeters are indispensable instruments to measure the energy of the collision products. For sampling hadronic calorimeters, choices relying on organic scintillators and wavelength-shifting (WLS) fibres read by photodetectors are successfull due to the low cost and are strong options for the future. Their operation under the expected harsher radiation conditions must meet crucial requirements of high light yield, fast response and radiation hardness. Although recent developments in organic scintillators/WLS indicate a breakthrough on light emission and time response, these emergent materials are lacking in R&D to scrutinise their radiation tolerance. This proposal includes R&D on the new organic scintillators/WLS, with the characterization of the light yield, attenuation length and resistance to ionising radiation. The work will be carried on at the LIP Laboratory of Optics and Scintillating Materials (LoMAC) and collaboration with national and CERN partners is expected. This research exploits also the current operation of the ATLAS Tile hadronic calorimeter to model the radiation damage of scintillators and WLS fibres using calibration data acquired in the real experimental environment. Several factors contribute to the total light output of scintillator+WLS fibre calorimeters, such as fibre length, scintillator plate/tile sizes, dose, dose rate and others. The plan will explore how these factors correlate with the light yield degradation using regression techniques based on modern machine learning and build tools to optimise the design of future detectors.

Development of data analysis methods for the observation of the Migdal effect

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1706 - Elias Lopez Asamar

Co-Supervisor: 267 - Francisco Neves

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

The existence of dark matter in the universe is considered one of the most clear indications of the possible existence of new physics not described by the Standard model. In this context, direct detection experiments aiming to search for dark matter particles that reach the Earth are of utmost importance. To date, direct detection experiments have typically searched for dark matter particles with mass above few GeV, but no conclusive signal has been observed yet. This fact has led to a very active area of research dedicated to develop new approaches to search for dark matter particles beyond the current experimental limits. One of such new approaches is based on the so-called Migdal effect, namely the predicted emission of an atomic electron when the respective atomic nucleus is perturbed. The exploitation of this phenomenon is considered as one of the most promising directions to search for dark matter particles with mass down to few hundreds of MeV. However the Migdal effect has not been observed yet. For this reason, a team of collaborating institutes that include Rutherford-Appleton Laboratory (UK), LIP-Coimbra and CERN (Switzerland) is developing an experiment to confirm the existence of such process. In this experiment, the Migdal effect will be induced in atoms of a gaseous target using fast neutrons. The purpose of this thesis is to contribute to the data analysis of such experiment. For this reason, the candidate will become a member of the respective collaboration. She or he will develop methods that will be applied to the collected data in order to search for events where the Migdal effect occurs. This work will include the exploration of machine learning techniques to identify the neutron-nucleus interactions where the Migdal effect occurs. This will involve to reconstruct the energy and the position of the particle tracks resulting from the neutron-nucleus interactions, and to develop discriminating algorithms that will allow us to identify the occurrence of the Migdal effect.

Is the neutrino its own antiparticle? - Probing the nature of the neutrino with the LZ dark matter detector

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 464 - Alexandre Lindote

Co-Supervisor: 617 - Claudio Frederico Pascoal da Silva

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

In a neutrinoless double-beta decay (0νββ), a nucleus with mass number A and charge Z undergoes the decay (A, Z) → (A, Z+2) + 2e− with no neutrinos being emitted. The observation of such a process is not allowed in the Standard Model of particle physics since it violates the conservation of the lepton number hinting that leptons play a part in the observed Universe matter/antimatter asymmetry. It would also probe the Majorana nature of neutrinos, i.e. neutrinos are their own antiparticles, and would provide information about the neutrino mass hierarchy and effective mass. As such the observation of this process would be a breakthrough in modern physics [1]. The corresponding two-neutrino double-beta decay (2νββ) is allowed and it has been observed for several nuclides. In particular, the nuclide Xe-136, which comprises 8.9% of naturally occurring xenon, has been shown to undergo 2νββ with a half-life of 2.2×10^21 years. The LUX-ZEPLIN (LZ) detector employs ten tonnes of liquid xenon to look for the interactions of dark matter particles [2] but it can also be used to look for 0νββ decay due to the large mass of the isotope Xe-136 present in the sensitive region of the detector (about 630 kg). A recent study using simulated data showed that we could reach a sensitivity of 1.06×10^26 years after 1000 days, similar to the best existing results [3]. However, this result had several conservative assumptions on both the background assessment, energy resolution, and background discrimination that can be significantly improved once the detector starts acquiring data during early 2021. The PhD candidate will look for this process in the LZ data and improve those assumptions as much as possible. This project also envisages the use of Machine Learning algorithms such as convolutional neural networks to explore the particular event topology of this decay, providing some efficiency to distinguish such decays from their main background. [1] Advances in High Energy Physics, 2016, 2162659 - "Neutrinoless Double Beta Decay: 2015 Review" [2] Phys.Rev. D101 (2020), 052002, arXiv:1802.06039 - "Projected WIMP Sensitivity of the LUX-ZEPLIN (LZ) Dark Matter Experiment" [3] arXiv:1912.04248 - "Projected sensitivity of the LUX-ZEPLIN experiment to the 0νββ decay of Xe-136"

Muon hodoscopes for cross-calibration of particle detectors

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 6 - Pedro Assis

Co-Supervisor: 29 - Ruben Conceição

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Astroparticle Physics observatories rely, in many cases, on the indirect detection of the primary particles reaching the Earth. The ground array technique uses particle detectors to detect the secondary particles produced in the interaction of the primary with the atmosphere. The correct estimation of the particle content is of the utmost importance. Several applications require the disentanglement of the several components of the particle pool: electromagnetic and muonic. For this, it has been deployed in the Pierre Auger Observatory a set of novel detectors to extract a correct and precise measurement of the muon component. However, the response of these detectors in field conditions is sometimes poorly known. LIP has been developing work to make a direct measurement using a dedicated detector based in the Resistive Plate Chamber technology. A spin-off has been a set of hodoscope instruments which have already been used in laboratory-like conditions to study the response of the main Auger detector. The challenge is to mount an RPC hodoscope in the field to define a muon beam. Such a beam could be used to study the response, in field conditions, of all the new detectors options being currently deployed. The thesis has a strong component in the instrumentation of RPC detectors and on the data-analysis of data produced.

Multiplicities of hadrons in Deep inelastic scattering in COMPASS experiment at CERN

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 472 - Marcin Stolarski

Co-Supervisor: 29 - Ruben Conceição

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Quarks are fundamental objects of the standard model of the particle physics. However, free quarks are not observed in nature. Always 2+ (anti)-quarks combine to produce hadrons. This process called quark fragmentation, and is of fundamental nature. In perturbative quantum chromodynamics (pQCD), it is effectively described by non-perturbative objects called fragmentation functions (FFs). Presently, these functions cannot be predicted by theory, they have to be measured experimentally. However, the pQCD predicts certain limits for the observed ratio of various produced particles. It come as a surprise that in COMPASS data the ratio of of negative to positive kaons is below the lower limit predicted by pQCD (in certain kinematic region). Presently, the origin of the discrepancy is not fully understood. The aim of PHD thesis would be to study in more detail the observed phenomena for pion, kaons and protons in data colleced by the COMPASS experiment at CERN. The analysis component of the work contains usage of Artificial Neural Networks. The grant holder is also expected to participate in COMPASS data taking in 2021 COMPASS is a high-energy physics experiment at the Super Proton Synchrotron (SPS) at CERN in Geneva, Switzerland. The purpose of this experiment is the study of hadron structure and hadron spectroscopy with high intensity muon and hadron beams.

RPCs in Astroparticle and their associated technologies

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 6 - Pedro Assis

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The LIP group participating in the Pierre Auger Observatory has been developing the Resistive Plate Chamber technology to be used in the context of Astroparticle Physics experiments. These are normally composed of distributed stations at remote locations and have stringent requirements on power, communications and price. Currently the RPCs developed have been working with no problems in the Pierre Auger Observatory site located in the Pampa Argentina at 1400 m of altitude. The solution developed has a good timing resolution of the order of the few ns (limited by the electronics and clock synchronization) but present a modest spatial resolution of the order of tens of cm. This resolution derives from the readout panel used composed of a matrix of pads with this size. In applications for the future detectors or for the detailed study of detectors response it is desirable to reach, at least, resolution of the order of the cm that allows to achieve angular resolutions better than the degree . The simplest way of increasing the resolution is to maintain the readout paradigm and simply reduce the pad size. However this would lead to a growth of the number of acquisition channels with the number of pads to the square. The aim of this thesis is to explore and develop solutions in which the increase on the resolution grows, at most, linearly with the factor gained in resolution. Changes can be considered at the detector level but solution will be investigated in the changing of the readout paradigm and on the instrumentation of the detector.

Quark propagator at finite temperature

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 301 - Orlando Oliveira

Co-Supervisor: 462 - Paulo Silva

Host Institution: CFISUC - Centro de Fisica da Universidade de Coimbra

Degree Institution: Universidade de Coimbra

PhD Program:

Typology: National

Quantum Chromodynamics (QCD) describes the interactions between quarks and gluons. One of the puzzling properties of QCD being that its fundamental particles, i.e. quarks and gluons, are not observed in nature but appear as constituents of mesons and baryons. In strong interactions two main open questions are the understanding of confinement (why there aren’t free quarks and gluons) and the mechanism that generates mass scales for quarks and gluons and that prevent infrared divergences. Current believe is that confinement and chiral symmetry breaking are interlaced. There are indications that for sufficiently high temperatures quarks and gluons behave essentially as a gas of free non-interacting particles, i.e. they seem to behave as deconfined particles. The formulation of QCD on a space-time lattice enables first principles determination of the quark and gluon propagators. From the propagators one accesses information about confinement/deconfinement and on the generation of mass scales, namely its running quark mass. The knowledge of the mass functions are crucial for the understanding of modern heavy ion experimental programs and for the history of the Universe. In this project we aim to compute, using the lattice QCD simulations, the quark propagator at finite temperature. The main goal is to help understanding chiral symmetry breaking and the confinement/deconfinement properties of QCD as a function of the temperature by studying the properties of the various form factors that define the propagator and looking at its spectral representation. The knowledge of the spectral representation allows also to investigate transport properties that are of paramount importance for the dynamical description of the heavy ion experimental programs. The simulations will be performed using mainly the supercomputer facilities at the University of Coimbra. The candidate will join a team with a large experience in lattice QCD simulations.

Modified gravity: Baryogenesis, Leptogenesis and Relic Abundances

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 111 - José Pedro Mimoso

Co-Supervisor: 466 - Francisco Lobo

Host Institution: IA - Instituto de Astrofísica e Ciências do Espaço

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Modified gravity predicts a different thermal evolution of the universe with respect to the one based on GR. More precisely, modified gravity predicts a modification (amplification) of the expansion rate of the universe with respect to the standard cosmology so that the thermal relics decouple with larger relic abundances. As a consequence, processes taking place during the highly energetic, very early universe such as baryogengesis and leptogenesis are sensitive to this modified cosmological behaviour. Moreover the correct values of the relic abundances are expected to come out from larger annihilation cross-section, which suggests that alternative cosmologies may contribute to explain values of the cross-section of thermal relics such as those of the PAMELA experiment. A systematic investigation of this topic is the main objective of the project.

Flavor Anomalies and New Physics

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The LHC physics program so-far has been extremely successful. It has established the standard model (SM) of particle physics as a superb theory. The SM cannot however be the ultimate theory of Nature, and a major goal of the LHC for the coming years is to detect the new physics (NP) that lies beyond the SM. The most significant and exciting indications of NP, in all of the current collider data, lie in what is referred to as the “flavour anomalies”. These have persistently emerged from the data of various experiments, with their significance enhanced considerably recently at the LHC. The anomalies imply a departures from Lepton Flavour Universality, a back-bone of the SM, thus having far reaching consequences. They are detected through measurements of b-quark decays to leptons. Such processes are highly sensitive to the presence of NP particles. The most favoured NP candidates are LeptoQuarks (LQ) and new gauge bosons (Z'). Even if those NP particles happen to be very heavy (and can thus not be produced directly in the LHC collisions), they contribute as intermediary states (as allowed by the Heisenberg uncertainly principle) and their presence becomes experimentally accessible in measurements of these sensitive B decays. The CMS detector has accumulated one of the largest heavy flavour datasets ever recorded. A dedicated data sample designed to facilitate the investigation of the above anomalies has been collected during 2018 by CMS. In this Thesis project the student will take part in the analysis of this dataset, and help in the prepration of the upcoming LHC run. The results that will be obtained will contribute to a clarification of the anomalies, which is a current main priority in the field of particle physics.

Associated production of heavy flavor

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 473 - Nuno Leonardo

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

The LHC has provided a wealth of sensitive data collected over the last decade, which has allowed to study the production and properties of standard model (SM) particles, resulting in precision measurements of the theory and to search for new particles beyond it. The data sets that are increasingly accumulated however allow for the study of rarer phenomena, a line of research that will be pursued with correspondingly increasing focus during the high luminosity phase we're entering. The associated production of SM particles, such as of quarks of different flavour, while considerably rarer than the inclusive production of the individual SM particles, facilitates a further level of understanding of SM particle production and of sensitivity to new states beyond the SM. The production mechanisms of double parton scattering and the intrinsic heavier quark content of the proton will be probed. The goal of this Thesis project is to study the associated production of beauty and charm quarks, benefiting from the very large heavy flavor data set that has been accumulated by the CMS experiment (that contains of the order of 10^10 b-hadrons, and a few times this number of c-hadrons). This shall be achieved by employing advanced data mining procedures to distinguish such rare signals from other the more ubiquitous SM backgrounds. Final states involving the exclusive decays of b (B,Y mesons) and c (D,Psi) mesons will be simultaneously reconstructed from the collisions' decay products. Extended unbinned likelihood statistical procedures will be implemented for extracting the underlying associated production cross sections, and in turn used to probe theory expectations. The mass spectra of the hadron pair will be formed and explored. The research will be carried in the frame of the activities of one of the outstanding research groups in High-Energy Physics in Portugal; citing the Report of the recent Institutional Evaluation performed by an international review panel nominated by FCT: “The LIP-CMS group, while small in size, is really outstanding and world-class”. The project is developed in collaboration between LIP and the Rio and DESY groups at CMS.

Testing modified gravity with black holes

Domain: Particle and Astroparticle Physics and associated scientific domains

Supervisor: 1735 - Jorge Rocha

Co-Supervisor: 1473 - Daniele Vernieri

Co-Supervisor: 170 - José Sande Lemos

Host Institution: CENTRA - Center for astrophysics and gravitation

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Despite the enormous success of General Relativity (GR) in describing gravitational phenomena, it faces serious conceptual challenges, most prominently the difficulty in reconciling it with quantum physics to yield a viable quantum gravity theory. At the same time it has proved hard to account for the huge amount of dark energy and dark matter inferred from cosmological observations without postulating ad-hoc additional fields that have so far been undetected. A profusion of extensions of GR have been proposed to address these problems, and among them several theories satisfy the (so far) scarce observational constraints imposed by the latest gravitational wave observations. How can one possibly determine which theories are the best candidates to supersede GR? Black holes (BHs) play a central role in this respect. Being hosts to the most extreme deformations of spacetime, they stand out as the ideal astrophysical laboratory to test gravity theories. Moreover, in recent years we finally obtained direct evidence for the existence of black holes, either through detection of gravitational wave signals produced during mergers, or through the observation of so-called black hole shadows. Nevertheless, black holes in modified theories of gravity generally differ from those of Einstein’s gravity and it is of utmost importance to understand their properties and behavior, and to quantify how their effects on gravitational wave observations depart from the predictions of GR. The aim of this research project is to explore black hole solutions in large classes of viable and well-motivated modified theories of gravity: we will mainly focus on Horndeski theories, Horava gravity and Einsteinian cubic gravity. In the context of these theories, the goal is to determine the tidal deformability of BHs, encoded in the so-called Love numbers, and to extract the time evolution of the geometry of the event horizon in a merging binary BH system. Both of these aspects leave crucial quantifiable imprints on the gravitational wave signals, which have not been explored so far. The scheme to complete this programme requires to extend and improve the theoretical framework to compute Love numbers.

Bragg Peak monitoring through prompt-gamma: detection and instrumentation

Domain: Technologies associated to the Portuguese participation at CERN and their transfer to society

Supervisor: 31 - Patricia Goncalves

Co-Supervisor: 1731 - Paulo Crespo

Co-Supervisor: 6 - Pedro Assis

Host Institution: Laboratório de Instrumentação e Física Experimental de Partículas

Degree Institution: Universidade de Lisboa

PhD Program:

Typology: National

Proton Therapy consists of the irradiation of tumors with a beam of energetic protons. Several advantages arise from the technique, being the main one the minimization of the dose given to health tissues surrounding the mass to be irradiated. In this technique it is common to use a “pencil” beam which can be moved in the XY plane. The protons on the beam will deposit small amounts of energy until they slow down and deposit a large quantity of energy in a limited region - the Bragg peak. The depth of the Bragg peak is closely related to the primary energy and as such it is possible to control the dose also in the z axis. However, other factors can influence the depth of the bragg peak and as such the monitoring of the Bragg peak position is of extreme importance. One of the techniques being considered is to perform the reconstruction of this zone by using prompt-emitted gammas from nuclear reactions of the protons with the tissues. This technique is a subject of dynamic research at LIP to establish the requirements, resolutions and best detectors to monitor the beam Bragg peak. LIP is currently involved in the development of prototypes for the detection of these gamma components. The main requirements is to be able to isolate prompt-gammas, using timing information on the order of the ns scale, and to reconstruct their origin. The current planned detector consists of a collimator to limit orthogonal directions to the beam and a set of particle detectors to sample the position. The instrumentation of the detector will have to deal with a high number of channels and a good timing granularity. However, the energy deposited in the detector may be disregarded and digital channel solutions can be considered. The work will consist of the participation of the simulation effort to understand the expected signals in the detector, the participation in the research prototype irradiation campaigns and the development of the solution for an industrial prototype.