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Study of the couplings between the Higgs boson and the electroweak gauge bosons in off-shell processes with the CMS experiment

par Mahdavikhorrami, Mostafa
Président du jury De Lentdecker, Gilles
Promoteur Vanlaer, Pascal ;Van Remortel, Nick
Publication Non publié, 2023-05-25

Thèse de doctorat

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Résumé :

This Doctoral research project focuses on investigating the Higgs sector in the off-shell regime, specifically through vector boson fusion (VBF) and gluon fusion (GF) Higgs production processes that decay into ZZ particles with 2l2nu final states. The study utilizes data collected at the Large Hadron Collider (LHC) between 2016 and 2018, within the framework of the Standard Model (SM) and the SM Effective Field Theory (SMEFT) using HVV anomalous couplings. The project is part of the hzz2l2nu group.Within the hzz2l2nu group, the primary research objective is to measure the width of Higgs decays and investigate HVV anomalous couplings at a high mass scale (off-shell). This analysis aims to impose stringent constraints on HVV anomalous couplings and the Wilson coefficient of dimension-six operators by leveraging the sensitivity of Higgs to ZZ to 2l2nu processes.The analysis is conducted using data obtained from the CMS experiment during LHC run 2 at a center-of-mass energy of 13 TeV, with an integrated luminosity of approximately 140 fb-1. The main focus of the analysis revolves around two signal processes: VBF/GF Higgs production that decays into ZZ particles, which subsequently decay into two charged leptons (electrons or muons) and missing transverse energy. The off-shell regime is achieved by selecting events with an invariant transverse mass (mT) greater than 200 GeV, representing the final state system's mass. By considering both changes in the Higgs decay width and the presence of anomalous couplings, it becomes necessary to constrain both parameters simultaneously due to their impact on the off-shell cross-section.Although the signal channels exhibit sensitivity to the off-shell Higgs decay production cross-section, an analysis combining the off-shell study with the on-shell analysis of H→ ZZ→ four charged leptons are required to constrain the width accurately. The width is inferred from the ratio of off-shell to on-shell Higgs production cross sections.As part of this Doctoral research project, a matrix-element (MELA) reweighting tool has been developed to simulate samples with both SM couplings and anomalous couplings, utilizing high-mass Higgs fully-simulated samples available in the CMS experiment.The planned objectives for this research project are to measure the Higgs decay width with the highest precision achievable at the LHC and to impose strong constraints on HVV anomalous couplings and Wilson coefficients in SMEFT. The contribution to this analysis mainly involves studying various observables in anomalous coupling samples at NNLO QCD + NLO EWK achieved through MELA reweighting and k-factors corrections.