Search for third-generation scalar leptoquarks with the CMS experiment

A search for pair produced scalar leptoquarks decaying into a top quark and a tau lepton using proton-proton collision data recorded in 2016 at a center-of-mass energy of 13TeV by the CMS experiment, corresponding to an integrated luminosity of 35.9fb$^{-1}$ is presented. The search is performed in final states with an electron or a muon, one or two hadronically decaying tau leptons, and additional jets. The data are found to be consistent with the Standard Model predictions. Upper limits on the production cross section are set as a function of the leptoquark mass. Leptoquark masses below 900GeV can be excluded at 95% confidence level, assuming a unity branching fraction of leptoquarks decaying into a top quark and a tau lepton. These results represent the most stringent limits for pair produced scalar leptoquarks in the top quark and tau lepton decay channel to date.The presented search is based on precisely calibrated jets. In the context of this thesis, jet energy calibration measurements based on proton-proton collision data recorded in 2015 at the CMS experiment, corresponding to an integrated luminosity of 2.1fb$^{-1}$ are presented. The calibrations are extracted from data and simulated events, and utilize dijet events to determine residual $|\eta|$-dependent data-to-simulation correction factors. The correction factors differ from unity by less than 3% in the central regions and up to 17% in the endcap and hadron forward regions of the detector.