Beschreibung:
Abstract: This thesis presents the measurement of the Higgs boson coupling to a pair of b-quarks. The H→bb̄ decay is predicted by the Standard Model to have a branching ratio of 58%, the largest among all decay modes. Therefore, accessing this decay is crucial to constrain the overall Higgs boson decay width.<br><br>The measurement is performed in the production process with a Z or W boson, whose leptonic decays ensure high rejection of the multi-jet background and efficient triggering of the signal signature. The analysis uses proton-proton collision data collected by the ATLAS experiment during the years 2015-2018, as produced by the Large Hadron Collider at a centre-of-mass energy of √s = 13 TeV, corresponding to an integrated luminosity of 139 fb-1.<br><br>The production of the Higgs boson in association with a Z or W boson is measured with an observed (expected) significance of 5.3 (5.1) and 4.0 (4.1) standard deviations, respectively, constituting the observation of the ZH process and the evidence of the WH one. The measured signal strength of µ(VH→bb̄ ) = 1.02+0.12/-0.11(stat.)+0.14/-0.13(syst.) is highly compatible with the Standard Model expectation.<br>Differential measurements of the VH, H→bb̄ cross section are performed as a function of the vector boson transverse momentum, yielding good agreement with theoretical predictions.<br><br>This thesis also presents performance studies of the impact of b- and c-hadron interactions with the ATLAS pixel detector material on the tagging efficiency of jets originating from b-quarks, known as b-jets. In addition, a new technique to identify b-jets without using tracking information is presented and it is expected to significantly improve the tagging efficiency at very high transverse momenta