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 reconstruction in the lepton plus jets decay channel using a simple and robust cut-based method has been studied. In particular, no b-tagging information was used. An in-situ jet calibration method was applied in order to minimise the systematic error due to jet energy scale. The reconstruction method is explained and its application on 145 pb−1 of simulated data is presented. Systematic effects and limitations of the method are discussed. Before applying the in-situ calibration, the dominant systematic error is found to be the jet energy scale as well as the combinatorial background. After applying the in-situ calibration, only the latter remains dominant. With a top quark mass of 172.5 GeV as input to the simulation, the method e.g. in the electron channel yields melectron t = 167.22 ± (2.38)stat (+4.07 −3.16)syst GeV. 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