Measurements of ttbar differential cross section at the ATLAS experiment in pp collisions at √s = 7 TeV and √s = 8 TeV

This PhD thesis presents two measurements of differential production cross section of top and anti-top pairs tt decaying in a lepton+jets final state. The normalise cross section is measured as a function of the top transverse momentum and the tt mass, transverse momentum and rapidity using the full 2011 proton-proton (pp) ATLAS data taking at a center of mass energy of √s=7 TeV and corresponding to an integrated luminosity of L=4.6 〖fb〗^(-1). The cross section is also measured at the particle level as a function of the hadronic top transverse momentum for highly energetic events using the full 2012 data taking at √s=8 TeV and with L=20 〖fb〗^(-1). The measured spectra are fully corrected for detector efficiency and resolution effects and are compared to several theoretical predictions showing a quite good agreement, depending on different spectra.