Search for the Higgs boson in the ttH(H->bb) channel and the identification of jets containing two B hadrons with the ATLAS experiment.

Abstract : Observing the Higgs boson production in association with a pair of top quarks (ttH) would allow a direct measurement of the top quark Yukawa coupling and provides an important test of the Higgs mechanism within the SM. This thesis presents a search for the Higgs boson in the ttH(H->bb) channel using proton-proton collisions at 13 TeV, collected with the ATLAS detector in 2015 and 2016. The Higgs boson de cays to two b quarks and top quark pair decays with one lepton, the ttH->(lνb)(jjb)(bb) single lepton channel, are considered. This document details in particular the contributions made by the author in this search: the full reconstruction of the ttH(H->bb) single lepton system and the fi nal discrimination between signal and the main background, tt +jets. A new method was developed to solve the large combinatorial background by fully reconstructing the ttH(H->bb) final state using a multivariate technique to uniquely associate each recon structed jets to the initial quarks. A multivariate technique was also used to discriminate between the signal and the main tt+jets background further increasing the sensitivity of the search compared to the Run 1 analysis. Finally, the first result at 13 TeV is shown. The signal strength (the ratio between the measured and predicted cross sections) is found to be 1.6 ± 1.1. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.6 (2.2) is set at 95% confidence level.
Keywords : LHC ATLAS Higgs boson
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Theses
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Contributor : Royer Edson Ticse Torres <>
Submitted on : Monday, May 1, 2017 - 1:33:49 AM
Last modification on : Thursday, January 18, 2018 - 1:55:11 AM
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Royer Edson Ticse Torres. Search for the Higgs boson in the ttH(H->bb) channel and the identification of jets containing two B hadrons with the ATLAS experiment.. Physics [physics]. Centre de Physique des Particules de Marseille, 2016. English. ⟨tel-01516435⟩

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