Measurement of the Z-boson mass, and simulation developments within the LHCb experiment at CERN

In the Electroweak (EW) sector of the Standard Model (SM), performing precision measurements of EW quantities and comparing them to values predicted by the SM is a stringent test of the current theory, and any discrepancy would hint towards new physics. In the SM, the Z-boson acquires its mass of around 91GeV through its gauge interaction with the vacuum energy of the Higgs field. Including higher order corrections the Z mass (mZ) is predicted with a precision of better than 10MeV, which corresponds to one part in 10,000. The Z mass was measured to 2MeV by the four LEP experiments in a beam-energy scan of the LEP e+e− collider. Meanwhile, hadron collider experiments have dominated the measurements of the W boson mass, but their studies of the Z boson mass have been primarily in the context of calibrations for the W mass analyses. This thesis presents the first dedicated Z boson mass measurement in protonproton collisions. The data were recorded in 2016 by the LHCb experiment and correspond to an integrated luminosity of 1.7 fb−1. The Z mass is determined from a fit to the dimuon mass distribution in Z ! μ+μ− decays. Templates from simulation are used in the fit, with a momentum calibration based on quarkonium resonance decays. The value of mZ is measured to be mZ = 91 185.7 ± 8.3 ± 3.9 MeV where the first uncertainty is statistical, and the second is systematic. This result is consistent with previous measurements and predictions from the Global Electroweak Fit (GEF). Future prospects are promising for future combinations of other experiments around the LHC, which could eventually challenge the LEP result. In addition, this thesis presents several contributions towards the simulation efforts in LHCb. The development of a new system to request simulation samples for analysis is presented, which has been deployed within the collaboration and saved countless hours and resources from experts and analysts alike. A new versioning framework has been developed to improve the detector model description for the collaboration, which has allowed parallel developments of di↵erent subdetector modules and unblocked development for future Upgrade II design studies.