Top Cross Section Ratios as Test of Lepton Universality in Charged Weak Decays in Proton-Proton Collisions at $\sqrt{s}+7$ TeV with the ATLAS Detector

In this thesis partial production cross sections of t t events are measured in four channels, dened by the nal state leptons from the decay of the W bosons and the triggering lepton, using 5 : 6 fb -1of data taken with the ATLAS detector at p s = 7 TeV. The di-lepton channel is dened as having one electron and one muon in the nal state. The lepton plus tau channels are dened as having a nal state electron or muon and one hadronically decaying tau. Partial cross sections for these channels are estimated, and ratios of partial cross sections, dened with the same triggering lepton, are calculated. The di-lepton events are divided into two non-exclusive channels dened by the presence of a trigger matched lepton. The production cross-sections of t t events with nal states including an electron and a hadronically decaying tau, or an electron and a muon, were measured and used to calculate their ratio R e = 0 : 65 +0 : 12 -0.10 (stat.) + - 0.18(syst.). The cross section ratio R e measured in data is compared to that inferred from the world average W and tau branching fractions, R Data e = R PDG e = 1 : 1 +0 : 21 -0.17(stat.) +-0.31(syst.) and is found to be consistent with unity.