Measurements of the Higgs boson produced in association with a vector boson and decaying to a pair of $b$-quarks with the ATLAS detector

The discovery of the Higgs boson in 2012 by the ATLAS and CMS experiments has opened a new research domain at the LHC, with the measurement of the properties of this particle to refine our understanding of the Standard Model and constrain physics beyond this model. The measurements of the Higgs boson decaying to a pair of $b$-quarks and produced alongside a $W$ or $Z$ boson, performed with the ATLAS detector using 139fb$^{-1}$ of data collected in proton-proton collisions at a center-of-mass energy of 13 TeV are presented in this thesis. Three channels are defined, the 0-, 1- and 2-lepton channels, depending on the number of charged leptons coming from the decay of the vector boson. The analysis takes advantage of the full Run-2 data statistics and of the improvement of many analysis techniques, which increase its sensitivity and yields the observation of the $ZH$ signal and a strong evidence of the $WH$ signal in this decay channel of the Higgs boson into pairs of $b$-quarks. Differential cross-section measurements are also performed and are found to be in good agreement with the Standard Model. The ATLAS detector will undergo many upgrades in preparation for the HL-LHC operation to be able to cope with the increase in luminosity and pile-up level. Therefore the liquid argon calorimeter readout electronics will be replaced. A part of this thesis is dedicated to check if the Front-End pre-amplifier prototypes proposed for the upgrade comply with the physics requirements.