Top Quark Mass Measurement With The ATLAS Detector

The uncertainty of the ttbar process modelling by the particle physics generators is evaluated. Evaluation is performed for the reconstruction of the top quark mass peak and the selection criteria of the ttbar events produced at the Large Hadron Collider (LHC). The mass peak reconstruction method and the ttbar event selection criteria considered for the analysis of the data collected with the ATLAS detector during the first year of the data taking are used for the uncertainty evaluation. For the position of the peak of the reconstructed top quark mass distribution and the for the selection efficiency the quantum chromodynamics (QCD) initial and final state radiation modelling uncertainties are demonstrated to be the dominant contributions to the signal modelling uncertainty. Based on the kinematic properties of the ttbar events the method for the reconstruction of the mass peak with reduced sensitivity to the QCD radiation effects is developed. A method for the separation of the jets from the ttbar hard process and the additional jets from the QCD radiation is presented. The jet multiplicity distribution is identified as an observable that can be used for the particle physics generators tuning with the early LHC data. Results are documented for the center of mass energies of collisions of 10 TeV and 7 TeV.