Heavy Flavour Jet Trigger using the ATLAS – Tilecal
IDPASC Portugal - PHD Programme 2017
2017 / 2018
Experimental Particle Physics
João Gentil Saraiva
Faculdade de Ciências - Universidade de Lisboa
Laboratório de Instrumentação e Física Experimental de Partículas
The Large Hadron Collider is colliding proton beams at the center of mass energy of 13 TeV and lead beams at 5 TeV. ATLAS is one of the four detectors built at the LHC to look into the smallest constituents of matter. It was designed to search for the Higgs boson of the Standard Model (SM) of Particle Physics and to search for new particles predicted by New Physics models beyond the SM in p+p collisions. ATLAS is also strongly involved in the Heavy Ion Program of the LHC in order to study the Quark Gluon Plasma, a state of matter in which quarks and gluons are no longer confined under the strong interaction. The LHC collides beam particles with a very high frequency, 40 MHz, but only a very small fraction is indeed interesting for physics analyses. The main role of the Trigger and Data Acquisition system of ATLAS is to select and store about 400 interactions per second for further analysis. In order to achieve this goal, the trigger system is divided in three levels. The first one is hardware based, while the two following use dedicated software algorithms to confirm the selection done by the first level trigger. One important problem is the high rate of fake muons originating in the beam halos, or by accidental coincidence of hits of charged particles, like protons, pions or kaons, in the muon spectrometer. These fake muons, in turn, produce high rate of fake heavy flavour jets (collimated sprays of particles) erroneously tagged as containing muons from B-meson decays. The Tile calorimeter outer layer can contribute significantly to eliminate these fake rates. In particular, the new read-out electronics of the calorimeter will improve significantly the signal to background ratio, enhancing the rejection of fake muons in a wide window of acceptance. The full integration of the new readout electronics is planned for the HL-LHC (after 2026). Prototypes are under development and are being put to test in testbeam with high energy particles. This data can already be used to study the performance of the new read-out electronics. The installation of some of these prototypes in ATLAS is foreseen for the following years and could be used than to develop a heavy flavour jet trigger using the Tile calorimeter in both first and subsequent trigger levels, by selecting hadronic jets containing a muon. The ATLAS-LIP group is strongly involved in the Tile calorimeter project since the very beginning, as well as in the jet trigger slice and jet physics analyses concerning p+p and Pb+Pb collisions. The student will explore a novel technique of using the outer layer of the Tile calorimeter of the ATLAS-LHC experiment for trigger purposes, in order to improve the efficiency and purity of Heavy Flavour Jets tagging. Furthermore, such a project implies the participation in LHC data acquisition, both p+p and Pb+Pb collisions, namely shifts and data quality monitoring. The project will contribute to the development of the ATLAS Upgrade trigger algorithms and, as such, will be integrated in the Software Upgrade program of the ATLAS experiment. The canditdate should have solid computing skills, namely in C++ programming, and must be available to travel to CERN for short periods (1, 2 weeks), several times in the year, for implementation tests.