Inclusive Z boson production and in association with b-jets in proton-proton collisions at 13 TeV with the ATLAS experiment

Abstract

In this thesis, the measurement of the inclusive Z-boson production cross section at the centre of mass energy of √s =13 TeV is first presented. The data analysed were collected by ATLAS during early Run 2 of LHC and correspond to a luminosity of 81 pb−1. The cross section measurement is performed separately in the electron and muon decay channels and in their combination. The ratio with respect to the W cross section is also performed in the same fiducial phase space, and it benefits from cancellation of some experimental uncertainties. Results are compared to NNLO calculations in perturbative QCD. The Z boson is then studied in associated production with at least one and at least two b-jets, using an enlarged dataset (36 fb−1) collected by ATLAS at the centre of mass energy of √s =13 TeV. Integrated cross sections are measured at the particle level for both the electron and muon decay chan- nels. Differential cross sections are measured as a function of the leading b-jet transverse momentum and rapidity, the Z boson rapidity and the an- gular separation between the Z boson and the b-jet. For events containing two b-jets at particle level, the cross section is measured as a function of the invariant mass and angular separation of the two highest transverse mo- mentum b-jets, and as a function of the kinematics of the sub-leading b-jet. Results are compared to LO and NLO Monte Carlo predictions. Finally, I present the work performed on the LUCID detector, the official ATLAS luminometer, to analyse calibration data with a 207Bi source, and the activity within the ATLAS muon performance group, to evaluate the muon reconstruction scale factors, using data acquired in Run 2.