Measurement of the top quark mass in the \(t\bar t \to {\rm lepton+jets}\) and \(t\bar t \to {\rm dilepton}\) channels using \(\sqrt{s}=7\) TeV ATLAS data

Abstract

The top quark mass was measured in the channels \(t\bar{t} \to \mathrm{lepton+jets}\) and \(t\bar{t} \to \mathrm{dilepton}\) (lepton=\(e, \mu\)) 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 \(t\bar{t} \to \mathrm{lepton+jets}\) 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 \(t\bar{t} \to \mathrm{dilepton}\) channel exploits a one-dimensional template method using the \(m_{\ell b}\) 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 \(172.33\pm 0.75(\rm {stat}) \pm 1.02(\rm {syst})\) GeV, and \(173.79 \pm 0.54({\rm stat}) \pm 1.30({\rm syst})\) GeV in the \(t\bar{t} \to lepton+jets\) and \(t\bar{t} \to dilepton\) channels, respectively. The combination of the two results yields \(m_{\mathrm top} = 172.99 \pm 0.48({\rm stat}) \pm 0.78({\rm syst})\) GeV, with a total uncertainty of \(0.91\) GeV.