Measurement of top quark pairs differential cross-sections at √s = 8 TeV with the ATLAS detector

In this poster, measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, tt system and event-level kinematic observables in proton–proton collisions at a centre-of-mass energy of √s = 8 TeV. The observables have been chosen to emphasize the tt production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3fb−1, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. The recorded events have been selected, through a cut based approach, in the single lepton (electron or muon) plus jets channel, with at least two of the jets tagged as originating from a b-quark. The most relevant background (QCD and W+ jets) have been extracted using data driven methods; the others (Z+jets, diboson and single top) have been estimated using Monte Carlo simulations. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The measurements are dominated by the systematic uncertainties and the results are in fair agreement with the predictions over a wide kinematic range. Most Monte Carlo generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. The agreement for this observable improves when next-to-next-to-leading order corrections are taken into account. The level of agreement for the rapidity distributions is improved when more recent sets of parton distribution functions are used.