Thesis

Study of top quark and Higgs bosons properties at the LHC

• Call:

  IDPASC Portugal - PHD Programme 2017

• Academic Year:

  2017 / 2018

• Domains:

  Theoretical Particle Physics | Experimental Particle Physics

• Supervisor:

  Antonio Onofre

• Co-Supervisor:

• Institution:

  Universidade do Minho

• Host Institution:

  LIP & University of Minho

• Abstract:

  In order to address the physics potential of the Large Hadron Collider (LHC) program, a significant joint effort of the experimental and theoretical community is required. This effort must not only consider the study of the best physical observables to perform a precise test of the Standard Model (SM) of particle physics at the LHC, but must also develop new ideas for physics beyond the SM. As such, the objective of the proposed research is to study several top quark and Higgs boson properties at the LHC in order to search for new physics effects, both from the phenomenological and experimental points of views, taking profit from the strong collaboration among the supervision team deeply involved in the ATLAS experiment at CERN. This research project will be supported jointly by the University of Minho and Institute de Recherche sur les Lois Fundamentales de l'Univers (IRFU) Saclay/Paris, member of the Paris-Saclay University, in great proximity with the theoretical group at the Borough of Manhattan Community College (BMCC) in New York with the goal of providing a general understanding of the current research in the field and of stimulating enthusiasm for scientific research. In this proposal, specific topics of the physics program of the LHC will be addressed from both the phenomenological and theoretical points of view, centered in two main tasks: 1. The objective of the first task is to study the main top quark decay to a W boson and a bottom quark. New analysis strategies and new observables (including angular distributions and asymmetries) will be proposed and studied in detail in order to probe new anomalous physics contributions to the Wtb vertex Lorentz structure. Strong collaboration between experimentalists and theorists is expected for this task, once the use and development of global fitters applied to top quark physics, like TopFit, are of utmost importance. The students supervision will be performed within a group with a long tradition of publishing in this area of scientific research. António Onofre was a former convener of the Top Quark Properties sub-group of the ATLAS experiment. During the execution of the work plan, foreseen stays, at IRFU,Paris-Saclay University, are expected to happen under the supervision of Frederic Deliot,who is currently the Top Quark group convener of the ATLAS experiment. Miguel Fiolhais is also expected to help on the students supervision, once he did his PhD in precise this type of measurements and can, at the same time, ensure an optimal bridge with the theoretical group at BMCC, New York. As was acknowledge recently by the team, combining all available experimental information concerning top quark physics and including more observables like new asymmetries (proposed in the literature but not measured yet by the experiments), is fundamental to achieve the best precision on the evaluation of the Wtb vertex structure, better then waiting by the end of all Runs at the LHC with only the few observables measured already. 2. The second task of this project is dedicated to the study of the associated production of the Higgs boson with a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. New angular distributions of the decay products, as well as angular asymmetries, will be explored in order to probe the CP nature of the Higgs coupling to top quarks, and reduce the contribution from the dominant irreducible background contributions. For this task, it is of utmost importance the bridge with the BMCC theoretical group, under a close supervision of Miguel Fiolhais once this gives the chance of understanding the production mechanism of ttH events at the LHC to NLO in fixed order perturbation theory with resummation of soft emission radiation to NLL accuracy. Although the applications for this specific call are for fellowships in the country (Portugal) IRFU and BMCC are currently considering covering the expenses for stays at those cites, during the execution of the current work plan, taking maximum profit from supervision expertise in all sites. The PhD degree expected at the end of the work plan, is to be attributed by the institutions involved, for which all necessary steps are under way.