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Measurements of standard model heavy particle production in association with jets using proton-proton collision data at 8 and 13 TEV with THE CMS experiment at the LHC

Bilin, Buğra
Standard Model (SM) of particle physics is the theory describing the main building blocks of matter and their interactions. In this thesis, two different measurements are carried out adding confidence to SM using proton proton collision data collected by the CMS experiment at the LHC . Within the first study, multi-dimensional differential cross section measurements are carried out with respect to several kinematic variables of Z bosons and jets, where the Z bosons are reconstructed from opposite sign lepton (electron or muon) pairs. This measurement using 8 TeV data is the most precise Z + jet cross section measurement among other hadron collision measurements up to now. Theoretical calculations using state-of-the-art techniques are compared with the CMS measurements obtained in this measurement, and therefore provided a stringent test of those calculations. It is proven here that calculations involving higher orders in QCD describe the CMS results better. Within the second study, measurement of Underlying Event (UE) activity accompa- nying top quark pair events is carried out using 13 TeV data. UE here corresponds to other parton collisions and remnants of protons accompanying the collision of phys- ical interest. Since UE includes non-perturbative QCD effects, it can not be exactly calculated, hence it is included parametrically into Monte-Carlo simulations. These parameters are "tuned" using existing experimental results. The validity of these tunes is proven in the highest known mass scale of particle physics, namely the top scale, in this study.