Measurement of the Single Top t-channel Cross Section Using a Cut Based Analysis With the ATLAS Detector in pp Collisions at √s = 7 TeV

Abstract

This thesis presents studies of the single top t-channel in the electron plus jets mode. In order to understand this channel, an account of the present theoretical models is given. This work relies on collisions data from the ATLAS detector and its components are presented here. A summary of the work involving the SCT, part of the tracking system in ATLAS, is also explained here. Studies were performed to optimize the measurement of the Lorentz Angle of the holes in the Silicon for the initial data taking period. The data studied was acquired by ATLAS during 2011, with a total integrated luminosity of 4.7 pb−1 at a √s = 7 TeV. Monte Carlo simulation of signal and background events was also used throughout. Background studies were performed to correctly determine the expected amount of QCD via the Jet Electron data-driven method and of light or heavy flavour jets produced in association with a W boson, which is one of the dominant backgrounds for the t-channel. A cut based analysis was then applied to the data and simulation in order to better discriminate the t-channel signal. A binned likelihood fit to the invariant mass of the reconstructed top quark was performed and the cross section value for the t-channel process was calculated: σt−channel = 62.2±8.0(stat)+8.6 −8.8(syst) pb which is in good agreement with the theoretically predicted value. Finally, the response (preco T /ptrue T ) of light quark or gluon initiated jets is evaluated for both the t-channel and the Wt associated production, in order to determine the flavour composition uncertainty, as part of the framework that provides the jet energy scale uncertainties in a multiple jets environment. Other sources of system- atics are also reviewed.