Search for bb¯ decay of the Stand Model Higgs boson produced in association with a vector boson (W/Z) with the ATLAS detector.

摘要

This dissertation presents a search for the bb¯ decay of the Standard Model Higgs boson. The analysis is performed with the ATLAS experiment, using the full dataset delivered by the LHC and recorded by ATLAS detector during LHC Run 1. The integrated luminosities used are 4.7 fb-1 at √s = 7 TeV, and 20.3 fb-1 at √s = 8 TeV. The processes considered in this analysis are associated (W/Z)H production, where W → ℓnunu, Z → ℓℓ and Z → nunu. Based on the number of leptons (ℓ), the events used in this analysis are divided into zero, one, and two lepton channels. In this analysis, no significant excess is observed above the Standard Model backgrounds. For mH = 125 GeV, a 95% CL upper limit of 1.4 times the Standard Model expectation is set on the cross section times branching ratio for pp → (W/Z )(H → bb¯). The corresponding expected limit is 1.3 in the absence of signal. The ratio of the measured signal yield to the Standard Model expectation is found to be mu = 0.2 +/- 0.5(stat.) +/- 0.4(syst.). This analysis procedure is validated by a measurement of the yield of diboson production(WZ and ZZ), with Z → bb¯. The ratio of observed diboson signal strength to the Standard Model expectation is found to be muD = 0.93 +/- 0.21, which is consistent with the Standard Model expectation of muD = 1.