Measurement of the fiducial differential cross-section of top quark pair production in the dilepton final state at 8 TeV.

The top quark is the most massive fundamental particle of the Standard Model of particle physics and being the only quark which decays before hadronization gives a unique opportunity for studying Quantum Chromodynamics (QCD). This dissertation presents a measurement of differential cross-sections of top quark pairs decaying in a purely leptonic mode as a function of the dilepton invariant mass, transverse momentum, difference in the pseudorapidity and azimuthal angle between two leptons in the same event at 8 TeV proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider. This data corresponds to an integrated luminosity of 20.3 fb−1. Events with top quark pair signatures are selected in the dilepton channel in the ATLAS acceptance (two leptons with pT > 25 GeV and |η| < 2.5). The measured cross-sections are compared to the Standard Model predictions generated using current Monte Carlo generators. All the measurements are found to be in agreement with the SM.