Measurements of the Higgs boson decaying into a b quark pair produced in association with a vector boson within the ATLAS experiment

The observation of the Higgs boson decaying into a $b$-quark pair was a major success of the LHC-Run2 data taking campaign. The leading sensitivity to this decay mode comes from events in which the Higgs boson is produced in association with a leptonically decaying vector boson. The analyses conducted so far only marginally involves $\tau$-leptons. $\tau$-particles can be produced through the $pp\to W(\tau\nu)H(b\overline{b})$ and $pp\to Z(\tau\tau)H(b\overline{b})$ channels, generating five different final state signatures depending on the nature (leptonic or hadronic) of the $\tau$-lepton decay. This thesis is mainly focused on the study and the optimization of the ATLAS VH(bb) resolved analysis, in which the Higgs boson transverse momentum is sufficiently low to allow to efficiently reconstruct the $H\to b\overline{b}$ final state using two separate $b$-tagged jets. A particular emphasis is given on the characterization of a new event category that includes for the first time events with hadronically decaying $\tau$ leptons. These studies are part of the ongoing effort on the precise determination of the $pp\to V(\text{lept.})H(bb)$ process by the ATLAS collaboration. Alternative analysis strategies exploiting the information on reconstructed hadronic-$\tau$ leptons, designed to optimize the current ATLAS VH(bb) measurements, are described as well as their expected improvements in terms of delivered signal strength precision and expected statistical significance