Measurement of single and double differential cross-section of top-quark pair production using data collected by the ATLAS detector in pp collisions at ps = 13TeV

In this thesis, measurements of the differential cross-section for top-quark pair production in proton-proton collisions at a centre-of-mass energy of ps = 13 TeV are presented. The measurements are performed using data collected by the ATLAS detector at the Large Hadron Collider at CERN during 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb−1. The top-quark pair events are selected in the lepton (electron or muon) plus jets channel and the analysis employs two separate selections and top-quark reconstruction strategies according to the value of the transverse momentum of the top quark. The single and double differential distributions are measured as a function of several kinematic variables of the top quark and the t ¯t system in a fiducial phase-space and extrapolated to the full phase-space. Given the large t ¯t production cross-section at the LHC, the measured spectra provide stringent tests of perturbative QCD and are relevant for the tuning of Monte Carlo simulations of the top-quark modelling. For this reason, the differential cross-section distributions are compared to several theoretical Monte Carlo predictions and state-of-the-art fixed-order QCD predictions