Description

The discovery of the Higgs boson by the CMS experiment marked a major milestone in particle physics, providing experimental confirmation of the Brout–Englert–Higgs mechanism responsible for mass generation in the Standard Model. Despite this success, the properties of the Higgs field and the detailed structure of the scalar sector remain only partially constrained. Improving the precision of Higgs boson measurements is therefore a central goal of current high-energy physics research.

The H→ZZ decay channel plays a key role in this effort, offering one of the cleanest and most sensitive experimental signatures for Higgs boson studies. This PhD thesis will focus on the study of the Higgs boson in the H→ZZ channel using proton–proton collision data collected by the CMS experiment during LHC Run 3 (2022–2026) at a center-of-mass energy of 13.6 TeV. The increased energy and integrated luminosity of Run 3 provide unique opportunities to improve the precision of Higgs production cross-section measurements, to probe its couplings to vector bosons, and to explore previously inaccessible kinematic regimes.

Achieving the required sensitivity will rely on the development of innovative signal extraction techniques, including advanced machine learning methods, as well as the optimization of event selection strategies. The combination of the results with data from previous LHC runs, as well as with those from the ATLAS experiment, is an important complement to this work. These studies will contribute to a more precise characterization of the Higgs field and to stringent tests of the internal consistency of the Standard Model.

In parallel with the physics analysis, the PhD candidate will contribute to the preparation of the High-Luminosity LHC (HL-LHC) era by participating in the Phase-2 upgrade of the CMS High-Granularity Calorimeter (HGCAL). This technical work will focus on the design and validation of advanced trigger primitive generation algorithms, capable of operating with low latency and high precision under extreme pileup conditions. These developments are essential to ensure the long-term performance of CMS for precision Higgs measurements, particularly in challenging channels such as H→ZZ.

Skills required

The CMS group at École Polytechnique is looking for a PhD candidate with a Master's degree (Master 2) in particle physics, who is interested in experimental high-energy physics. A basic knowledge of C++ and Python is recommended.

Bibliography

CMS Collaboration, 'A portrait of the Higgs boson by the CMS experiment' Nature 607 (2022) 60
https://arxiv.org/abs/2207.00043

Physics of the HL-LHC, and perspectives at the HE-LHC
https://e-publishing.cern.ch/index.php/CYRM/issue/view/94

`Optimizing the performance of the CMS Electromagnetic Calorimeter to measure Higgs properties during Phase I and Phase II of the LHC`
A. Zghiche, International Journal of Modern Physics A, 2020, World Scientific

`An overview of more than ten years of operation of the CMS ECAL`
A. Zghiche, International Journal of Modern Physics A, 2024, World Scientific

New development in the CMS ECAL Level-1 trigger system to meet the challenges of LHC Run 2
Floris Thiant et al., Proceedings of Topical Workshop on Electronics for Particle Physics — PoS(TWEPP2018), 2019, Sissa Medialab

'The Phase-2 Upgrade of the CMS L1 Trigger Interim Technical Design Report', CERN-LHCC-2017-013 ; CMS-TDR-017,
https://cds.cern.ch/record/2283192

'The Phase-2 Upgrade of the CMS Endcap Calorimeter', CERN-LHCC-2017-023 ; CMS-TDR-019, https://cds.cern.ch/record/2293646

Keywords

Higgs Boson, LHC, High Granularity Sampling Calorimetry, Trigger, Machine Learning, CMS Experiement