Study of ATLAS sensitivity to the single top s-channel production

The single top production can be divided into three different mechanisms, each with its own distinct final state topology and background. At the LHC, these events will be produced at about a third of the rate of top quark pairs. Moreover, the precise determination of the corresponding cross sections is sensitive to physics beyond the Standard Model, suggesting the top quark as an excelent place to look for 'new physics'. In this thesis, the sensitivity of the LHC ATLAS experiment to the mea- surement of the single top s-channel process cross section, for a low luminosity of $200 pb^{−1}$ of data, was studied. In order to simulate the early data period of LHC, the full simulation (FullSim) of the detector was used, at a center- of-mass energy of $sqrt{s} = 7, m{TeV}$. The signal events were generated by the MC@NLO generator, as well as most of the background events. The other background samples were generated using either ALPGEN or HERWIG. The selection of the single top quark events was developed in a sequencial and a discriminant analysis, maximizing the efficiency of event selection and back-ground rejection. From the obtained results, a limit on the single top s-channel production process was estabilished at $95%$ Confidence Level.