PhD position: "Origin of matter/antimatter asymmetry with top quarks and CMS tracker upgrade for HL-LHC" - IP2I (UMR 5822)

Short description

The PhD position is proposed for a 3-year period (36 months). The legal gross salary is €1768 per month (plus social benefits). An annual €2 000 package for travels and equipment will be allotted. The candidate is expected to submit a thesis manuscript to the university of Lyon for a formal presentation in front of a jury before the end of the 3-yr period.

Starting date of the contract: October the 1st, 2021

Research project

The observable Universe is made primarily of matter and not antimatter, while both should be equally produced at the big-bang: this is one of the most intriguing puzzles of modern physics. CP symmetry (symmetry under inversion of the electric charge and spatial reflection), mirroring particles and antiparticles, is a key piece in this puzzle. This PhD thesis will contribute to understand the origin of matter/antimatter asymmetry, using top quarks as a precision probe to search for CP violation in proton-proton collisions at the LHC.

The light quark sector of the Standard Model (SM) exhibits CP violation in an amount far too small to explain the observed matter/antimatter asymmetry. However in some light quark processes (b->s transition) involving top quarks in quantum corrections, tensions were recently shown between theory and experiment, which may be a first indirect hint of new physics. The top quark is the heaviest elementary particle, suspected to play a major role beyond the SM. Therefore a direct precision measurement of CP violation with top quarks is urgent, and will be carried out within this project.

The LHC is the most powerful top quark factory ever built, which provided about 125M top-antitop (tt) events and 45M events of single tops at LHC Run 2. The PhD student will analyze LHC data of Run 2 and Run 3 (2022-2024) collected at the CMS experiment, and will focus on single top events, extremely sensitive to CP violation. To push the precision beyond world-leading results, the PhD student will use the large LHC dataset available; employ advanced analysis techniques with deep learning; and work on the reduction of the systematic uncertainties.

Continuing in the future with the quest of understanding the origin of mass, and solving the mystery of matter/antimatter asymmetry, will require to upgrade the CMS detector for the High Luminosity LHC (HL-LHC), whose start is planned for 2027. The current CMS tracker will need to be completely replaced for the HL-LHC, to sustain the radiation level induced by the large increase in LHC luminosity. The PhD student will participate in the CMS tracker upgrade, a work carried out at IP2I within the LIO Clean Room.

During the duration of the PhD thesis, the LIO Clean room will be mainly used for the construction of the future tracker mechanical structures (so-called ‘Dees’) and their integration. These operations comprise Dee production, Dee mechanical and thermal qualification, the mounting of the silicon detector modules onto the Dees and a battery of detector module tests. The PhD student will bring crucial expertise in analysis, working with engineers and technicians. The task will consist in the data analysis of Dee mechanical and thermal tests, and performing module tests with its subsequent analysis.

The PhD student activities will be shared approximately at 50/50 between physics analysis and instrumentation.