Search for resonance in the photon$+$jet final state at $\sqrt {s}$ = 13 TeV using the CMS detector at LHC

The Standard Model, that describes the fundamental particles and their interactions, is a very solid and elegant theory, verified in many independent experiments. However there are still many reasons to believe it is incomplete. To name some: the theory does not incorporate gravity; it does not explain the asymmetry of matter and antimatter in the universe; similarity in three families of fermions. There are several models of new physics that predict the existence of resonances at the TeV scale, and therefore accessible at the proton-proton collisions of the LHC. The new resonance searches presented in this thesis are narrow resonances decaying to a photon and a jet. If such a resonance exists, the experimental signature will be a bump corresponding to the mass of the resonance over the smoothly falling invariant mass distribution of photon and jet. In this thesis, proton-proton collision data collected by CMS experiment corresponding to an integrated luminosity of 138 fb$^{-1}$ is used. The potential backgrounds are estimated using data-driven techniques and excess of events above the standard model background predictions are investigated. No evidence for the existence of new particles is observed relative to expectations from the standard model. Hence, upper limits on production cross-section times branching ratio and lower limits on the mass of excited quarks and Quantum Black Holes, predicted by the BSM models, are placed at a 95% confidence level. The thesis also presents the installation of Gas Electron Multiplier (GEM) in CMS muon system, as an upgrade of CMS detector for HL-LHC. The GEM detectors are installed in the forward region of the muon system to improve the muon reconstruction and the trigger rate. The Panjab University participated in the assembly and testing of the GEM detectors for muon upgrade. A brief summary of the assembly procedure and testing setup is presented in this thesis.