Search for Higgs boson in the $WW^{(\ast)}$ channel in ATLAS and drift time measurement in the liquid argon calorimeter in ATLAS

A Higgs search is performed in the W W → lνlν channel using the full 2011 data at a center-of-mass energy of sqrt(s) = 7 TeV and part of 2012 data at 8 TeV taken by the ATLAS experiment at the LHC. The corresponding integrated luminosity values are 4.7 fb−1 and 5.8 fb−1 , respectively. The cut based analysis is performed and several data-driven methods for background estimation are introduced. The jet veto survival probability method for top background estimation in 0-jet bin is proposed and used in the Higgs search. Another data-driven method to correct missingET shapes in the Drell- Yan process is also presented. In 2011, the standard model Higgs boson with the Higgs mass from 133 to 261 GeV is excluded at 95% CL, while the expected exclusion range is 127−234 GeV. In 2012, an excess of events over expected background is observed at mH = 125 GeV. Combining both samples, the minimum observed p0 value is 3 ×10−3 , corresponding to 2.8 standard deviations. The fitted signal strength at mH = 125 GeV is μ = 1.4 ± 0.5. The expected p0 for a Higgs with mH = 125 GeV is 0.01, or 2.3 standard deviations. The exclusion limit for a Higgs in a fourth generation model is shown using part of the 2011 data sample, the mass range between 120 GeV and 600 GeV has been excluded at 95% CL. The study of the drift time in the liquid argon calorimeter in ALTAS is performed using all special data samples from cosmic muons, beam splash and beam collision data. The results show no significant non-uniformity on the cell gap width and a sagging effect due to gravity is observed.