Differentiating top-quark. Photon coupling: Inclusive and differential cross-section measurements of top-quark pair production in association with a photon in the single lepton channel in pp collisions data at √s=8 TeV with the ATLAS experiment

This thesis presents measurements of inclusive and differential production cross sections of top- anti-top-quark pairs in association with an additional prompt photon (t anti tγ) in the single lepton final state at the LHC analysing data recorded by the ATLAS detector. The data analysed corresponds to 20.2 fb^-1 of integrated luminosity recorded during 2012 at a center-of-mass energy of √s=8 TeV. The cross.section is measured with a template fit method. Background processes are estimated with data driven and Monte Carlo based methods. The differential cross section is measured as a function of transverse momentum and pseudo-rapidity of the photon. A total of 1256 and 1816 candidate t anti tγ events are observed in the electron and muon channel, respectively. Both inclusive and differential measurements are performed in a fiducial phase space within the detector acceptance. The differential measurements are performed as a function of transverse momentum and pseudo-rapidity of the photon. The inclusive t anti tγ production cross section times the branching ratio (BR) is measured to be σ_{t anti tγ} x BR=71.4±13.0 fb in the electron channel. The measured cross section in the muon channel reads σ_{t anti tγ} x BR=70.0±9.8 fb. The results are in agreement within the uncertainties with the corresponding Standard model predictions at next-to-leading order.