Search for the Higgs boson decaying to b quark pairs in the W/Z associated production channels with ATLAS

In 2012, the ATLAS and CMS experiments at CERN discovered the Higgs boson with an approximate mass of 125~GeV in LHC pp collisions at $\sqrt{s} =$ 7 and 8~TeV center of mass energy. Given the very large branching ratio to b-quark pairs (58\%), the $H\rightarrow bb$ decay measurement is fundamental to determine the boson decay width and couplings and to confirm the SM hypothesis. However, the bb production cross-section in $\sqrt{s} =$ 8~TeV pp collisions is 7 orders of magnitude greater than the Higgs production cross section, making the $H\rightarrow bb$ decay one of the most challenging searches at the LHC. In fact, this decay was not yet observed and the Higgs couplings to down-type quarks are still to be measured. In the associated production in which the Higgs is produced with a W/Z boson, the leptonic decay of the W/Z is used to trigger the event and substantially reduce the backgrounds. The ATLAS Run I search for the $H\rightarrow bb$ in the W/Z associated production is presented here. The data set used correspond to integrated luminosities of 4.7~$fb^{-1}$ at $\sqrt{s} =$ 7~TeV and 20.3~$fb^{-1}$ at $\sqrt{s} =$ 8~TeV.