Étude du couplage du boson de Higgs au quark top dans les canaux avec deux leptons de même signe avec l’expérience ATLAS au LHC

Abstract : The Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) enables physics exploration at subatomic level and restarted in June 2015 with a centre of mass energy of 13 TeV. The first part describes the electron reconstruction efficiency measurement with the ATLAS detector using 27.7 fb^-1 of data collected in 2016. Precise measurements of lepton efficiencies are crucial in the LHC hadronic environnement. Electrons reconstruction efficiency is computed in both data and Monte Carlo simulation samples for all ATLAS physics analyses to use. It varies from 97% to 99% with an accuracy at the percent and per mille level at low energy and E_T>20 GeV, respectively. The second part focuses on the Higgs boson coupling y_t to the top quark. Seven multileptonic channels from the associated production of the Higgs boson with a top quark-antiquark pair (ttH) are studied using 36.1 fb^-1 of data collected in 2015 and 2016. The focus is done on the most sensitive one for the measurement, with a two same-charge leptons final state. Background discrimination is based on machine learning with multivariate analysis (MVA) techniques. Combining all ttH analyses, the ATLAS and CMS experiments independently claimed an evidence, and then the observation of the ttH process. The same methodology has been used in the search for flavour changing neutral currents in top-quark decays in the 2lSS and 3l channels. Upper limits on the branching ratios B(t->Hu) and B(t->Hc) have been set to 0.16% and 0.19%, respectively, and are currently the most stringent ones.
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Kevin de Vasconcelos Corga. Étude du couplage du boson de Higgs au quark top dans les canaux avec deux leptons de même signe avec l’expérience ATLAS au LHC. Physique des Hautes Energies - Expérience [hep-ex]. Aix-Marseille Université, 2018. Français. ⟨tel-01941954⟩

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