Search for a standard Higgs boson in the W H channel with the D0 detector at the Tevatron

The Higgs mechanism provides the Standard Model with an appropriate theory of the origin of the mass of gauge bosons and elementary fermions. The Higgs boson has not yet been discovered, but a lower limit on its mass has been set at 114.4 GeV at 95 % confidence level by the Lep collaborations. Higgs searches are now being pursued at the Tevatron, a proton - anti-proton collider with a centre-of-mass energy of 1.96 TeV. At low mass the most sensitive channel is the associated production of a Higgs with a W boson. An analysis has been performed in the decay channel in which the Higgs goes into a bb-bar pair and the W decays to a muon and a neutrino with 1 fb-1 of Run-IIa data recorded by the D0 detector. The analysis relies on all the sub-detector components but most particularly on the calorimeter which is essential for reconstruction of the bb-bar system. Good tracking and a b-identification neural network tool provide improved b-tagging performance which is crucial for this analysis. Because the energy resolution of jets is of paramount importance when hunting for a two-jet resonance bump, work has also been conducted on devising a better-performing calibration for jets which exhibit a muon and a neutrino in their fragmentation chain. The W H analysis is performed on a W+2 and W+3 jet event topology. Events containing a muon, missing transverse energy and two or three jets are selected; the jets are then b-tagged. The double-tagged and single-tagged channels are analysed separately so as to provide additional sensitivity. Signal-background separation via a neural network algorithm has furthermore been developed in the analysis in order to enhance sensitivity. This search for a standard Higgs boson has been conducted for Higgs masses ranging from 100 GeV to 150 GeV. Upper limits on production cross-section times branching ratio have been set. For a Higgs mass of 115 GeV, the upper limit is set at 2.00 pb at 95 % confidence level in the channel W H →μνbb-bar and 1.37 pb when combining the two channels W H → μνbb-bar and W H → eνbb-bar, which is to be compared to the theoretical prediction of 0.136 pb. (author)