Description du sujet de thèse

The thesis will take place inside the ATLAS and FCC collaborations. The ATLAS experiment is installed at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. The LHC Run3 data taking (2022-2026) will integrate more than 300 fb-1 of pp collisions at 13.6 TeV by the end of 2026. The following runs will correspond to the high luminosity operation until 2041 aiming to accumulate 3000 fb-1 ("high luminosity phase"). This large sample of data will allow the first observation of di-Higgs production and access to the self-coupling of the Higgs boson, but also the measurements of the Higgs boson couplings to other elementary particles with few % precision, which could further validate (or invalidate) the predictions of the Standard Model.
To continue the study of the Higgs boson with higher precision, beyond HL-LHC, an e+e- “Higgs factory” project is being recommended as the priority for the European particle physics community after the LHC. Such Higgs factory could be the Future Circular Collider (FCC) project, which will use e+e- collisions in its first phase (FCC-ee) and proton- proton collisions in a second phase. Detectors with excellent particle reconstruction and identification performance will be needed to achieve a precision well better than 1% on the different couplings of the Higgs boson. Currently several R&D projects to develop detectors that can provide the necessary performance are underway.
This thesis will be divided in two parts:
a) the analysis of the ATLAS Run3 data for the search of the production of two Higgs bosons for the measurement of its self-coupling, decaying in bb tautau, with the ATLAS data from Run3, with an optimization of the sensitivity of the analysis compared to Run2 and the use of multivariate analysis techniques to maximize the separation between signal and background. We are targeting to have first evidence for this process with the larger dataset, improved analysis techniques of Run3 compared to Run2 and combination of the different channels of ATLAS and CMS results. The measurement will put constraints on the self-coupling of the Higgs boson and on models of physics beyond the Standard Model. The candidate will also give a contribution to the activities of the team on the software needed of the future tracking detector (ITK) for the high-luminosity upgrade of the LHC.
b) In addition, the candidate will contribute to the ongoing Higgs physics feasibility and detector R&D studies on FCC-ee. The expected measurements of ZH production, Higgs self-coupling, and of the Higgs boson mass at FCC-ee will be studied in detail. These expected Higgs measurements will be used as benchmarks to compare the performance of different detector designs and layout currently under study.

Contexte de travail

The Astroparticles and Cosmology (APC) laboratory is a joint research unit involving the CNRS-IN2P3 and the Université Paris-Cité in particular, with an average staff of around 200. The person recruited will work in the ATLAS/FCC group, which is made up of 3 permanent physicists and 4 non-permanent physicists. The person recruited will also be required to work in collaboration with members of the ATLAS Collaboration outside the laboratory. Regular missions to CERN are to be expected as part of the research project, to take part in collaboration meetings and potentially in detector operations.
The work is expected to result in one or more scientific publications. Communications via posters or public presentations at conferences are also planned. All results obtained as part of the ATLAS and FCC Collaborations are required to be open access once published, as are the algorithms used.
The candidate should have an engineering degree and/or a master's degree in particle physics or a similar field. The position requires a solid knowledge of programming, good oral and written communication skills (French and English required) to present at conferences and write articles in scientific journals. We are looking for a young researcher who is committed to the project, curious, with a degree of autonomy and strong motivation to develop their skills and complete their thesis work within 3 years. Candidates should also be able to work as part of a team on multidisciplinary projects.
Other qualities required: good writing skills, ability to formulate and manage a scientific project, ability to work in a team. Experimental internships in particle physics desirable

Contraintes et risques

The thesis will be attached to the Step'up ED560 doctoral school.
Travel to CERN for scientific missions is to be expected.