Search for high-mass dimuon resonances and study of endcap muon system neutron-induced background hits with the Compact Muon Solenoid detector

This thesis presents a search for narrow resonances in the dimuon invariant mass spectrum using data obtained from proton-proton collisions at $\sqrt{s}=13$ TeV collected by the CMS detector at the CERN LHC. We describe the analysis and results of the data collected in 2018, which corresponds to an integrated luminosity of 63.1 fb$^{-1}$. We also present results of the combination of the 2016, 2017, and 2018 data sets, as well as the results of the combination with the dielectron analysis, which correspond to a total integrated luminosity of up to 140 fb$^{-1}$. The results are interpreted in terms of the upper limit on the ratio of the cross section of a new resonance to that of the $Z$ boson. We also compute the corresponding lower limits on the masses of various benchmark resonances. No evidence for beyond the standard model physics is observed in the 2018 data set, or in any of the combined data sets. Relevant for the high masses where we perform our search, we also discuss the reconstruction and performance of high momentum muons in CMS. In the appendix, we present a study of neutron-induced background hits in CMS endcap muon chambers.