Prospects for the measurement of the top quark mass in ATLAS

The prospects are presented for a top-quark mass, mtop, measurement via the template method using the channel ttbar->lepton+jets based on early ATLAS data. Two variants of the template analysis are presented, a 1-dimensional template analysis for very early data with an integrated luminosity, Lint, of up to 100 inverse pb, and a 2-dimensional template analysis optimized for Lint of up to 1 inverse fb, the luminosity expected from the upcoming 2010−2011 LHC run. The 1-dimensional template analysis explores the stabilized top-quark mass, mstab, to minimize the impact of the jet energy scale, JES, uncertainty on mtop. This is advantageous, since the JES is expected to be precisely known only after larger sets of ATLAS data have been collected. The 2-dimensional analysis uses b-tagging, as well as a kinematic fit of the decay products of both top-quarks, and simultaneously extracts mtop and the JES from the data, thereby offering a more precise determination of mtop, while requiring a better understanding of the detector. With the 1-d template method, and combining the ttbar->electron+jets and ttbar->muon+jets channels, a measurement of mtop with a statistical precision of about 2.0 GeV and a systematic precision of about 3.8 GeV is expected for sqrt(s) = 10 TeV and Lint = 100 inverse pb. With the 2-d template method, and using 1 inverse fb of data in the combined channel, the statistical precision is about 0.6 GeV and the system atic precision about 2.0 GeV.