Prospects for measuring the differential high pT b-jet cross section with the ATLAS detector

Currently, the Large Hadron Collider (LHC) at CERN in Geneva accelerates protons up to an energy of 3.5 TeV resulting in collisions of a center-of-mass energy of √s = 7 TeV. To study the production of b-quarks in proton-proton collisions is part of the physics program of the ATLAS experiment, which is one of the experiments at the LHC. The b-quarks produced in the hard scattering of the protons are measured as jets in the ATLAS detector. The aim of this PhD thesis is to study prospects of a differential pT b-jet cross section measurement in the jet pT range of pTjet > 30 GeV. This study is based on simulated Monte Carlo (MC) data assuming a center-of-mass energy of √s = 10 TeV. The trigger selection is based on a combination of single jet triggers considering the different prescale factors of the different jet triggers. The MC data samples contain signal b-jets and background jets from other QCD physics processes in the proton-proton collision. In order to identify the b-jets and to reject background jets, b-tagging algorithms based on the on average longer lifetime of particles containing a b-quark compared to other hadrons, which decay before reaching the detector, are used. Since the b-tagging performance is not uniform over the jet pT region con- sidered, different b-tagging efficiency scenarios are studied. The jet pT independent b-tagging efficiency scenarios of ǫT ag = 0.5 and ǫT ag = 0.6 as well as an optimized b-tagging efficiency scenario in order to minimize the statistical uncertainty of the measurement in each jet pT bin are presented. An unfolding algorithm is applied to the measured b-jet spectrum in order to correct for detector effects due to the measuring process. The expected systematic uncer- tainties for different jet pT regions are studied and an estimate for the evolvement of the statistical uncertainties as a function of the integrated luminosity is given. Once an integrated luminosity of at least 100 pb−1 has been collected the differential b-jet cross section at the ATLAS experiment can be measured up to pTjet < 750 GeV. For 750 GeV < pTjet < 1.1 TeV an integrated luminosity of approximately 400 pb−1 is needed to reduce the statistical uncertainty to the level of the systematic uncer- tainty. The systematic uncertainty is dominated by the uncertainty of the jet energy scale calibration of the calorimeters. The systematic uncertainties vary from about 25% in the lower jet pT region to about 50% in the higher jet pT region.