Search for the Higgs boson in the WH channel and production of Wbb-bar in 1.96 TeV pp-bar collisions in the D0 experiment at the Fermilab Tevatron

The introduction of the Higgs boson in the standard model provides a mechanism to explain the origin of the masses of the elementary particles. 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 LEP experiments. The search for the Higgs boson has been pursued at the Tevatron, proton-antiproton collider, in the associated production channel WH with a Higgs mass lower than 135 GeV where the Higgs decay in bb-bar. The detector D0 is used to record the signals. For this analysis, the calorimeter and the tracker are the main sub-detector. The signals from the calorimeter have been studied through a calibration and a study on the noise level in order to improve the reconstruction of the objects. The missing transverse energy, the electrons and the jets are well identified objects so they can be used in our analysis W(→ eν) + jets. As D0 has a new tracker and solenoid system, information from this system allow us to tag jets when they are originating from a b-quark. The analysis of events W(→ eν) + 2*b-tag jets has been made on 174 pb-1. An upper limit of the cross section production of the process W(→ eν)bb-bar has been derived at 20.3 pb at 95% confidence level. This process is the main irreducible background of the WH → eνbb-bar. In the second part of the analysis, the search for the Higgs boson has been done for different mass values between 105 GeV and 135 GeV. Upper Limits on cross section production times branching ratio have been set. For a Higgs mass of 115 GeV, the upper limit is set of 12.4 pb at 95% confidence limit. (author)