Prospects for the measurement of the top-quark mass with early ATLAS data

The prospects are presented for a top-quark mass, mtop, measurement in the ttbar -> letpon+jets channel via the template method using early ATLAS data. Two variants of the template analysis are presented. A 1-dimensional template analysis which adopts the stabilized top-quark mass, mtopstab, exploiting the event-by-event ratio of the reconstructed top-quark and W boson masses associated to the hadronically decaying top quark candidate, to minimize the impact of the jet energy scale, JES, uncertainty on mtop. A 2-dimensional analysis which simultaneously extracts mtop and the JES from the data. The latter, making uses of b-tagging, as well as of a kinematic fit of the decay products, offers a more precise determination of mtop, while requiring a better understanding of the detector. The 1-d analysis is optimized for very first data with integrated luminosities, Lint, up to 100 inverse pb; whereas the 2-d analysis up to Lint of 1 inverse fb, the total integrated luminosity currently expected from the upcoming 2010-2011 LHC operations.