Recherche d'un boson de Higgs charge avec le detecteur ATLAS : de la theorie a l'experience

This thesis is intended as a bridge between the two highly specialised domains of phenomenology and experimental particle physics. The first part describes in detail a higher order cross section calculation and implementation into a Monte Carlo event generator. We present the calculation of the next-to-leading order (NLO) quantum chromodynamic corrections for charged Higgs boson production in association with a top quark at the LHC, using the Catani-Seymour dipole subtraction method. Building an independent NLO code enabled us to cross-check the implemented version of MC@NLO, and a few studies have been made which focus on different contributions to the theoretical uncertainty attached to the NLO calculation. The actual implementation was performed for another NLO event generator, POWHEG. Considering the small production cross section of charged Higgs production associated with a top quark, an analysis of this channel using the 35 pb-1 of data collected with the ATLAS detector in 2010 from the proton-proton collisions of the LHC, makes no sense, and we switch to a very similar SM channel, namely Wt production. In the second part, we set-up a dedicated analysis for semileptonic Wt and focus on the evaluation of the PDF systematic uncertainty, following the PDF4LHC recommendation. The electroweak single top production cross section at the Tevatron is so low that it hasn't been observed until today, so we are able to set the world's first limit on its production cross section and include the most important systematic uncertainties in our analysis.