Search for Quark Compositeness in gamma+jet final states in proton-proton collisions at sqrt(s) = 13 TeV with the CMS Detector at the Large Hadron Collider

The main aim of the particle physics is to investigate the fundamental buildingblocks of matter and the forces governing them. Within the context of the standardmodel of particle physics, quarks and leptons are considered to be fundamental.Their existence have been verified by a number of experiments and their propertiesare extensively studied. In spite of its great success, the standard model is notconsidered as a complete theory. There are a number of unexplained phenomenawhich predict the existence of some new physics beyond the standard model. Theexistence of three nearly identical generations of quarks and leptons strongly suggestthe possibility of an underlying sub-structure. A variety of models, referred to as,the compositeness models, are theorized which consider the quarks and leptons to bemade up of more fundamental particles, known as “preons”. A convincing signatureof the quarks sub-structure is the observation of their excited states. These excitedquarks are supposed to interact with their standard model counterparts through√gauge interaction for the compositeness scale, Λ ≤ s. Various searches have beenperformed in the past to observe excited states but no evidence has been found.This thesis presents a search for the excited states of light u, d and heavy bflavor quarks in the γ + jet and γ + b-jet final states respectively, using the pp√collision data at s = 13 TeV, collected by the CMS detector in 2016. This datacorrespond to a total integrated luminosity of 35.9 fb−1 . The excited quark signals,if exist, will show their presence in the form of bumps over the continuous invariantmass distribution spectrums of γ + jet and γ + b-jet states respectively. Manystandard model processes can also imitate these final states, thereby, formingthe backgrounds of this study. This analysis has two main backgrounds comingfrom SM γ + jet and QCD dijet processes, with a small contribution from W/Z +jet processes. The MC samples corresponding to these backgrounds are used tovalidate the data as per the standard model expectations. The actual backgroundof this study has been obtained by using a data driven technique. The excitedquarks signals are generated and simulated using the event generator pythia toscan a broad mass range.In the absence of any expected signal, upper limits on the cross-sections or lowerlimits on the masses of excited quarks have been set at the 95% confidence levelusing the frequentist approach in the asymptotic approximation. A comparison ofxiii