Measurement of the top quark mass in the tt̄→ lepton+jets t t ¯ → lepton+jets and tt̄→ dilepton t t ¯ → dilepton channels using √s=7 s = 7   TeV TeV ATLAS data

The top quark mass was measured in the channels t t lepton+jets and t t dilepton (lepton = e, ) based on ATLAS data recorded in 2011. The data were taken at the LHC with a proton-proton centre-of-mass energy of s = 7 TeV and correspond to an integrated luminosity of 4.6 fb -1 . The t t 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 t t dilepton channel exploits a one-dimensional template method using the m b 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 + JSF + bJSF) 1.02(syst) GeV, and 173.79 0.54(stat) 1.30(syst) GeV in the t t lepton+jets and t t dilepton channels, respectively. The combination of the two results yields m top = 172.99 0.48(stat) 0.78(syst) GeV, with a total uncertainty of 0.91 GeV.