First simultaneous measurement of single and pair production of top quarks in association with a Z boson at the LHC

In the years 2016–2018 the CMS Experiment at CERN's Large Hadron Collider recorded a large amount of proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb${}^{-1}$. With this large dataset, the associated production of top quarks with the Z boson has been measured precisely and differentially. In this thesis, for the first time, single and pair production of top quarks in association with a Z boson (tZq, tWZ and $t\overline{t}$Z) are measured simultaneously and differentially. A multiclass deep neural network is used to separate the signal processes and the backgrounds. The interference between $t\overline{t}$Z and tWZ complicates their separation, and therefore their sum is reported in the results. Compared to previous studies, the simultaneous measurement is less dependent on the signal modeling assumptions and improves the sensitivity to new physics scenarios, as it enables to constrain possible deviations from the standard model across different processes. Studies on muon identification methods with the CMS detector are also presented, with particular focus on novel techniques to correct discrepancies between simulation and the data.