Search for Wt-channel single top quark production in 7 TeV proton-proton collisions using the ATLAS detector

The production of single top quarks through the weak interaction is of great interest in particle physics, as it provides the only means to directly measure the CKM matrix element |Vtb|, one of the few remaining Standard Model parameters which has yet to be precisely constrained by direct experimental measurements. This thesis describes a search for Wt-channel single top quark production using proton-proton collision data collected at a center-of-mass energy of 7 TeV by the ATLAS detector at the Large Hadron Collider, corresponding to a total integrated luminosity of 35 pb-1. Collision events having exactly two oppositely-charged electrons or muons, a single high-transverse-momentum jet, and large missing or total transverse energy are selected, resulting in a sample with enhanced single top purity. 38 data events are found to survive the selection, in good agreement with the expected sum from all signal and background predictions of 38.6+-6.0. The Wt content of the selected sample is predicted to amount to 4.3+-0.3 events. The resulting cross-section measurement is sigma(pp->Wt) = 10 +20-10 (stat) +20-10 (syst) pb. As this level of precision is insufficient to claim evidence or discovery of this process, an upper limit is also derived for the parameter of interest, resulting in sigma(pp->Wt) < 70 pb at 95% condence level.