Measurement of the top quark mass using lepton transverse momenta with the ATLAS detector at √s = 8 TeV

The mass of the top quark is determined in proton-proton collisions at a centre- of-mass energy of 8 TeV, recorded by the ATLAS experiment at the LHC. For the measurement, tt¯ events with lepton+jets final states are used. A top quark decays almost exclusively in a bottom quark and a W boson, therefore the lep- ton+jets channel represents the decay in which one W boson decays hadronically and the other one leptonically. In contrast to other measurements, this analysis is designed to exploit the dependence of the lepton kinematics on the top quark mass, by parameterising the lepton’s transverse momentum distribution with MC simulations. Applied for the first time on 8 TeV ATLAS data, this method can complement other mtop measurements, because of its different sensitivity to sys- tematic uncertainties. With this approach, the top quark mass is measured to be 167.6 ± 0.9 (stat) ± 2.1 (syst) GeV. The total uncertainty of 2.4 GeV results from a careful evaluation of various systematic sources. Since the result depends on the modelling of the top quark transverse momentum, it is sensitive to higher order corrections. The influence of such corrections is estimated by reweighting the NLO MC prediction to NNLO calculations. This results in a shift in the measured top quark mass of −1.0 ± 0.5 GeV and there- fore shows that higher order corrections can have a significant influence in the determination of mtop with the lepton pT.