Etude de la production associee ZH/WH, H → tautau avec le detecteur ATLAS

In the Standard Model, a doublet scalar Higgs field is predicted leading to the presence of a neutral scalar particle, the Higgs boson. The LEP experiments have set a lower bound on the Higgs mass at 114.5 GeV. The electroweak precision measurements constrain indirectly the SM Higgs boson mass to be below 154 GeV at 95% of confidence level [2]. In this mass range, the Higgs boson decay into photons is one of the most important channels for the search of this boson at LHC. It benefits from the good resolution of the electromagnetic calorimeter of the ATLAS detector and the background is manageable. This process suffers, however, from a very low branching ratio. That is why each of the production channels has to be considered. Here, we evaluate the possibility to use the associated Higgs production with a Z or W boson. The cross-sections of these processes are low but the signal over background ratio is better than the inclusive analysis. The associated Higgs production can be used to increase the statistical significance of the Higgs boson discovery. The associated production modes can also be used to measure the Higgs couplings to the weak bosons.;Two types of background events are considered in the analyses. Among the ir-reducible backgrounds, we have, for instance, weak boson production with two photons from SM processes or heavy quarks (c, band t) with two photons. The reducible background contributions include, for example, processes which underestimate the energy of a hadronic jet, producing artificially missing energy.;We have chosen to separate events depending on their topology because, by combining the different analyses, we have a better statistical significance. Because of the low signal cross-section, the results suffer from high theoretical, systematic and statistical uncertainties. These analyses are sensitive, in particular, to tails of reducible background distribution, which are difficult to evaluate. Nevertheless, we estimate that we can observe the signal with a significance equal to 2.9 for a Higgs mass equal to 120 GeV after 30 fb -1 of integrated luminosity.;Keys words: ATLAS, particle physics, Higgs, associated production, Standard Model;We have taken into account the leptonic and hadronic decays of the weak bosons and we have developed analyses depending on the event topology. In each analysis, we require two high momentum photons which should come from the Higgs boson decay. The first analysis looks for events containing one isolated lepton (electron or muon) with missing energy to reconstruct the WH events. The second analysis looks for high missing transverse momentum to select ZH events when the Z boson decays into neutrinos. The last one, very preliminary, analyzes the case where events contains two hadronic jets coming from the hadronic decay of the weak bosons.