Standard Model Higgs Boson Searches in the Weak Boson Decay Channels with the ATLAS Detector

The search of the Standard Model Higgs boson decaying into a pair of weak bosons with the subsequent leptonic decay of the W or Z bosons is presented. The contributions achieved by this work range from the réévaluation of Higgs boson normalisation cross-sections, to the development of the analysis strategies using detailed Monte Carlo simulations and the search results for the H -► ZZ -► l+l-ννbar decay mode based on 4.7 fb-1 of proton-proton collision data at sqrt(s) = 7 TeV taken during 2011 by the ATLAS detector. The computation of cross-sections values for Higgs boson production at centre-of-mass energies varying from 6 to 14 TeV, for the main production mechanisms at the LHC were documented for posterior usage among the Collaboration. Preliminary detector resolution studies on Z -► μμ events using early data collected by ATLAS are also described. Simulation studies for the H -► ZZ(*) -► l+l-l+l- and H — W+W- — l+νl-ν channels included feasibility checks used to quantify the expected sensitivity of the analyses for various scenarios with different centre-of-mass energy, luminosity and detector calibration conditions. These results were part of the input that the Collaboration used to feed the schedule and plans of the LHC. On the H -► ZZ -► l+l-ννbar channel, upper limits on the Higgs boson production cross-section in a mass range between 200 and 900 GeV are set. With this channel by itself, the Standard Model Higgs boson particle is excluded at 95% confidence level in the mass range between 319 and 558 GeV To complete the current picture of the Higgs boson searches in the ATLAS detector, a compilation of the different Higgs boson analyses performed by the ATLAS Collaboration are introduced. The Higgs boson existence is constrained to be in a narrow window between 122.5 GeV and 129 GeV with 95% confidence level; where an excess of 2.6 a local significance is observed.