Measurement of the Inclusive Electron Cross-Section from Heavy Flavour Decays and of the Bottom Production Rate with the ATLAS Experiment

This thesis presents a measurement of the inclusive electron production cross-section from heavy-flavour decays with the ATLAS experiment at the LHC. A dataset of proton-proton collisions at a center-of-mass energy of 7 TeV with a total integrated luminosity of 1.28 +- 0.04 pb-1 is used for this measurement. Signal electrons, arising predominantly from semi-leptonic decays of charm and bottom hadrons, are extracted using a binned maximum likelihood method. A combination of particle identification techniques is used to discriminate against the dominant backgrounds of hadron fakes and photon conversions. Taking into account trigger, reconstruction and identification efficiencies, the extracted inclusive electron spectrum is unfolded into a differential cross-section as a function of the electron transverse momentum. A good agreement is found with theoretical predictions and with an ATLAS measurement using muons in the final state. The integrated cross-section for electrons originating from heavy- flavour decays, in the transverse momentum range 7 < peT < 26 GeV and within the pseudorapidity range |eta_e| < 2, excluding 1.37 < |eta_e| < 1.52, is sigma^e_HF = 0.946 +- 0.020 +- 0.146 +- 0.032 microbarns. A study of the production rate of bottom hadrons, based on the same dataset as the inclusive measurement, is also presented. The relative pT of the electron with respect to a nearby track-jet, p_T^rel, is used in a binned maximum likelihood fit to differentiate the bottom hadron signal from charm, light hadron and photon conversion backgrounds. The spectrum of electrons from bottom decays as a function of the electron reconstructed ET is compared to LO and NLO MC predictions.