Studie zur Bestimmung der Top-Quark-Masse ueber den Zerfall der B-Hadronen in dileptonischen ttbar-Ereignissen mit dem ATLAS-Experiment am LHC

A Monte Carlo study of the top quark mass determination with the ATLAS experiment at the Large Hadron Collider (LHC) is presented. The decay vertex of the B hadrons in ttbar events is reconstructed and four different observables, connected to this vertex, are defined. These observables are the decay length, the thrust, the mean decay angle and the mean opening angle and they are all related to the B hadron momentum. Because of kinematical reasons, each of them is sensitive to the top mass. Due to the fact, that one only requires tracking information for every observable, the top mass determination is independent of the jet energy scale, which is a common, crucial uncertainty of the other methods used so far. At the LHC eight million top quarks will be produced per year at an integrated luminosity of 10e33 cm−2 s−1. Therefore the dilepton channel, which has a lower cross section but a higher signal-to-background ratio than the other channels, is considered. For every observable the statistical and systematic errors of the top mass are estimated, whereas the full detector simulation is used. The statistical error is found to be approximately 1 GeV for all observables. For the decay length the systematic error is estimated as 5 GeV and for the other observables between 5 GeV and 6 GeV.