Search for the Higgs Boson decaying to a b quark pair produced in association with a W Boson using missing transverse energy triggered events at ATLAS

The WH → lvbb production and decay mode of the standard model Higgs Boson is searched for using the 2012 LHC proton-proton data recorded by the ATLAS detector at a centre-of-mass energy √s=8 TeV. Events containing W → μv that fail muon triggers are recovered using a novel technique of recording these events with missing transverse energy based triggers. Two analyses are employed, one based on simple selection criteria to enhance the signal-to-background ratio and one that uses more complex multivariate techniques to separate signal from background. Both analyses exploit the different signal-to-background ratios in regions of the reconstructed W transverse momentum and b-jet tagging categorisation. The events recorded using the missing transverse energy triggers are analysed exclusively as well as merged with the events recorded using lepton triggers to improve the sensitivity of the final analyses. The multivariate merged analysis is found to be the more sensitive of the two analyses, gaining 18.5% compared to the equivalent cut-based analysis. The observed (expected) 95% CL limit for the WH → lvbb mode is found to be 2.507 (1.369) and the observed (expected) significance is 1.905 (1.534). The final value of the signal strength for WH → lvbb is μ=1.231± ^{0.733}_{0.665} which is consistent with the Standard Model expectation.