Measurement of the cross-section for b-jets produced in association with a Z boson at sqrt(s) = 7 TeV with the ATLAS detector

Abstract

In this thesis, 4.7 fb^(-1) of data taken in 2011 by the ATLAS Experiment of proton-proton collisions at sqrt(s) = 7 TeV delivered by the Large Hadron Collider at CERN is used to measure the integrated and differential cross sections for the production of electroweak Z bosons in associaton with b quark jets. Z bosons are identified by reconstructing the electron and muon decay modes, and the fraction of b quark jets in the Z sample is estimated by fitting the neural network output of a specialised heavy flavour tagging algorithm in data with light + charm and bottom flavour templates derived from Monte Carlo simulation. The integrated Z + b jet cross section is measured to be 5.04 +- 0.17 stat +- 0.83 syst pb. The ratio of the integrated Z + b jet cross section to the inclusive Z production cross section is measured to be (5.26 +- 0.18 stat +- 0.89 syst) 10^(-3). The integrated Z +b jet cross section is also measured differentially in bins of b jet transverse energy, b jet rapidity, and Z boson transverse momentum. These measurements are compared to predictions from leading order Monte Carlo generators and next-to-leading-order QCD calculations. Also contained within this thesis are contributions to the commissioning of the ATLAS detector with early data, and studies produced for the calibration of software algorithms used in the tagging of heavy flavour jets. The resolution of the ATLAS inner detector is measured using data recorded by ATLAS in 2009. Systematic effects resulting in discrepancies between the efficiency to identify heavy flavour jets in data and simulation are measured using 2010 ATLAS data