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Search for light scalar particles from Higgs boson decays in exclusive final states with two muons and two hadrons at the CMS experiment

par Dansana, Soumya
Président du jury Vanlaer, Pascal
Promoteur Clerbaux, Barbara ;Lowette, Steven
Publication Non publié, 2025-12-15

Thèse de doctorat

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Résumé :

The Standard Model of particle physics has been remarkably successful in describing matter and its interactions at the subatomic scale. There are, however, few key observations that do not fit within the framework of the Standard Model, such as the existence and the nature of dark matter. Theoretical extensions, termed as Beyond Standard Model (BSM) theories, often propose new particles that can be produced in high-energy experiments such as CMS at the LHC collider. In this thesis, a search for new scalar particles of $mathcal{O}(mathrm{GeV})$ mass in exclusive final states with muons and light hadrons is presented. The search targets exotic decays of the Higgs boson to a pair of prompt or long-lived identical scalar bosons with proper decay lengths up to 100 mm and masses within the range of 0.4--2.0 GeV. This mass window corresponds to a unique phase space where hadronic decays mostly consist of only pairs of light hadrons. The analysis uses proton-proton collision data produced at the LHC in 2016--2018 at a center-of-mass energy of 13 TeV and collected by the CMS detector. The analysis achieves unique sensitivity to very light scalar boson masses and demonstrates a novel approach to probe hadronic decays of light scalar bosons. In parallel, a study of the jet energy resolution at the CMS experiment is carried out using the 2018 dataset to contribute to ongoing jet calibration efforts. A validation study comparing two different methods used within the CMS Collaboration is also performed as part of this work.