PhD position « Origin of matter/antimatter asymmetry with top quarks and CMS tracker upgrade for HL-LHC »

PhD position « Origin of matter/antimatter asymmetry with top quarks and CMS tracker upgrade for HL-LHC »

France 01 May 2021


In 2011, Lyon Institute of Origins (LIO) LabEx was selected following the first Laboratory of Excellence call for projects, part of the Investissement dAvenir program for forward-looking research.
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01 May 2021
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Short description

The PhD position is proposed for a 3-year period (36 months). The legal net 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 (1/2 page – 1 page)

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.

Research field(s)

Particle physics

Thesis supervisor and contact

Name: Nicolas Chanon

Laboratory: Institut de Physique des 2 Infinis de Lyon (IP2I)

Phone number: +33 4 72 44 85 01


Working environment

Job location and description

The PhD student will be based at the IP2I, will be a member of the CMS IP2I group and become a member of the CMS experiment at CERN, signing all CMS publications. Activities will be shared between CMS data analysis and instrumentation.

If pandemic permits, frequent travels at CERN are foreseen, to participate in meetings, present analysis results and perform tasks required by the CMS Collaboration at the detector. The work on tracker upgrade is done in collaboration with UCLouvain and DESY (Hambourg), where travels are also foreseen.

Results will be presented in national workshops and international conferences.


N. Chanon is currently co-supervising one PhD thesis (50%, end Sept. 2021) and one post-doc.

The physics analyses will be performed within the CMS group of IP2I. The main supervisor will be N. Chanon (CR).

In addition, the instrumentation activities of the thesis will be performed in collaboration with engineers from the Instrumentation group at IP2I, and researchers from the CMS group involved in the project. Direct participation from: Massimiliano Marchisone (IR).

Allocated resources (technical facilites, computing…)

The PhD student will have access to CERN computing element and storage, the LCG grid, the Tier-1 computing center of CC-IN2P3 on the campus (including a GPU farm for training deep learning methods), and to the Tier-3 of the IP2I.

Instrumentation activities will be performed within LIO Clean room on the site of IP2I.

Recent publications of the team

1) CMS Collaboration. Measurement of the Higgs boson production rate in association with top quarks in final states with electrons, muons, and hadronically decaying tau leptons at √s =13 TeV. arXiv:2011.03652 [hep-ex]. Submitted to EPJC, 2020.

2) CMS Tracker Collaboration. Beam test performance of prototype silicon detectors for the Outer Tracker for the Phase-2 Upgrade of CMS. 2020, JINST 15 P03014.

3) A. Carle, N. Chanon, S. Perries. Prospects for Lorentz Invariance Violation searches with top pair production at the LHC and future hadron colliders. arXiv:1908.11256 [hep-ph]. Eur.Phys.J. C80 (2020) no.2, 128.

4) J. Lee, N. Chanon et al. Polarization fraction measurement in ZZ scattering using deep learning. arXiv:1908.05196 [hep-ph]. Phys. Rev. D 100, 116010 (2019).

5) J. Lee, N. Chanon et al. Polarization Fraction Measurement in same sign WW scattering using Deep Learning. arXiv:1812.07591 [hep-ph]. Phys. Rev. D 99, 033004 (2019).

6) CMS Collaboration. Observation of ttH production. arXiv:1804.02610 [hep-ex], Phys. Rev. Lett. 120, 231801 (2018).

7) CMS Collaboration. Evidence for associated production of a Higgs boson with a top quark pair in final states with electrons, muons, and hadronically decaying τ leptons at √s = 13 TeV. arXiv:1803.05485 [hep-ex], JHEP 08 (2018) 066.

8) CMS Collaboration. Measurement of the associated production of a single top quark and a Z boson in pp collisions at √s = 13 TeV. arXiv:1712.02825 [hep-ex]. Phys.Lett. B779 (2018) 358-384.

Description of LabEx LIO

In 2011, The Lyon Institute of Origins LabEx was selected following the first “Laboratory of Excellence” call for projects, part of the “Investissement d’Avenir” program for forward-looking research. It is one of 12 LabExes supported by the University of Lyon community of universities and establishments (COMUE). LIO brings together more than 200 elite researchers recruited throughout the word and forming 18 research teams from four laboratories in the Rhône-Alps region, all leaders in their fields, under the auspices of the University Claude Bernard Lyon 1 (UCBL), the Ecole Normale Supérieure de Lyon, and the CNRS. LIO’s goal is to explore questions about our origins, operating in a broad field of study that ranges from particle physics to geophysics, and includes cosmology, astrophysics, planetology and life.

Selection process

The successful candidate will be selected in partnership with the Doctoral School « Physics and Astrophysics » of the University of Lyon.

Condition for admission to doctoral studies

The candidates must hold a national master degree or equivalent.

Application deadline

May the 1st, 2021

Requested documents for application

The candidates must submit their application with (i) their academic curriculum of the last three years, (ii) a letter of motivation, (iii) a CV and (iv) a letter of recommendation, to before May the 1st, 2021.

Candidates on the short list will be informed by the end of May. They will be interviewed in June.

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