Search for Anomalous Single Top Quark Production in Association with a Photon in pp Collisions at $\sqrt{s}$ = 8 TeV

This thesis reports the results of a first search for the flavor-changing neutral current(FCNC) through the anomalous production of single top quark in association witha photon due to the anomalous interactions of tqγ (q = u or c) in pp collisions. Thissearch is performed using 19.8 fb−1 of data collected with the CMS detector at thecenter-of-mass energy of 8 TeV.In this study we only concentrate on the muonic decay of the W-boson in topquark decay. The search is conducted in final states with an isolated muon, anisolated photon, jets, at most one of which is consistent with originating from theevolution of a b quark, and missing transverse momentum, corresponding to topquark decays, in which the W boson from the top quark decay is detected in the µν.A multivariate classification approach is chosen to achieve a powerful discrimination between signal like events and standard model backgrounds. No evidencefor the FCNC processes are observed. Upper limits at 95% confidence level on thestrengths of the anomalous couplings are found to be κtuγ < 0.025 and κtcγ < 0.091.The corresponding upper bounds on the branching ratios are Br(t → uγ) < 0.013%and Br(t → cγ) < 0.17%. The obtained upper bounds are the most stringent limitup to date.Upper limits on the signal cross sections are also reported for a restricted phasespace region to provide results that can be more easily compared with theoreticalpredictions. Observed upper limits on the cross sections are found to be 47 fb and39 fb at 95% CL for tuγ and tcγ production, respectively. The restricted phasespace defined similarly to the final analysis phase-space and requiring exactly oneidentified b jet in the data. These are the first results on anomalous tγ productionwithin a restricted phase-space region.Keywords: