The Standard Model is the framework which allows to describe interactions between particles and their dynamics. The Higgs mechanism is a solution to naturally introduce a mass term in the theoretical description of this model. After electroweak spontaneous symmetry breaking, a new massive scalar particle is introduced, the Higgs boson. Since it hasn't been discovered yet, the search for the Higgs boson is carried at the Tevatron, which is a pp collider at a center-of-mass of 1.96 TeV. For MH < 115 GeV, the dominant decay mode is H → bb ̄ . The analysis presented in this document is focused on the 100 < MH < 150 GeV mass range, in the channel where the Higgs boson is produced in assocation with a W boson which decays either to an electron or muon and a neutrino. The study of this final state relies on informations collected from all parts of the DØ detector. A result based on 5.3 fb−1 of RunII Tevatron collisions is presented here. In order to increase the sensitivity to the signal, the analysis is separated in different sub-channels according to the lepton flavour, number of jets in the final state, number of jets identified as originated from b quarks and data taking periods. After selecting events, a multivariate analysis technique is used to separate signal-like events from the expected physics and instrumental backgrounds. A good agreement between data and simulation is observed. As no signal excess is observed in data, an observed (expected) upper limit of 4.5 (4.8) for MH = 115 GeV is set on the ratio of the W H cross section multiplied by the H → bb ̄ branching fraction to its standard model prediction, at 95% confidence level. Since the final Tevatron dataset is soon to be analyzed, an effort is brought to achieve the maximum sensitivity. A preliminary analysis updated in Summer 2011 is presented as well as future improvements to be considered in the final publication for the search in the WH → lνbb ̄ channel. Since the dijet invariant mass is the most discriminant single variable, a correction based on jet shapes is derived to improve the mass resolution, hence the analysis sensitivity. Moreover, a different usage of b-jets identification tools and optimization studies on the final discriminant yields a significant improvement. This result is part of the Tevatron Higgs combination.
