Top Quark Mass Measurement: Prospects of Commissioning Studies for early LHC Data in the ATLAS Detector

A study to prepare a top quark mass measurement with early LHC data was carried out. The top quark is reconstructed in the lepton plus jets decay channel using a cut-based method. In particular, no b-tagging information was used. The analysis is applied on 145 pb^-1 of simulated data and e.g. in the electron channel yields m_t = 167.22 &plusmn (2.38)_stat(^+4.07_-3.16)_syst GeV. Systematic effects and limitations of the method are discussed. The dominant systematic error is found to be the jet energy scale as well as the combinatorial background. After an in-situ jet calibration method is applied, only the latter remains dominant. <br> First real data - both from cosmic muons and from LHC single beams - are used to study the in-situ performance of the ATLAS calorimeter system. Also included are calibration measurements of the electronics readout system. They yield a detector test of the expected calorimeter performance.