Measurement of the top quark mass in the ttbar -> lepton+jets and ttbar -> dilepton channels using sqrt(s) = 7 TeV ATLAS data

The top quark mass was measured in the channels tt¯→lepton+jets and tt¯→dilepton (lepton=e,μ) based on ATLAS data recorded in 2011. The data were taken at the LHC with a proton--proton centre-of-mass energy of sqrt(s) = 7 TeV and correspond to an integrated luminosity of 4.6fb−1. The tt¯→lepton+jets analysis uses a three-dimensional template technique which determines the top quark mass together with a global jet energy scale factor (JSF), and a relative b-to-light-jet energy scale factor (bJSF), where the terms b-jets and light-jets refer to jets originating from b-quarks and u,d,c,s-quarks or gluons, respectively. The analysis of the tt¯→dilepton channel exploits a one-dimensional template method using the mℓb observable, defined as the average invariant mass of the two lepton+b-jet pairs in each event. The top quark mass is measured to be 172.33±0.75(stat)±1.02(syst) GeV, and 173.79±0.54(stat)±1.30(syst) GeV in the tt¯→lepton+jets and tt¯→dilepton channels, respectively. The combination of the two results yields mtop=172.99±0.48(stat)±0.78(syst) GeV, with a total uncertainty of 0.91 GeV