Search for single vector-like quarks with the CMS detector

In this thesis, proton-proton data is analysed in search of singly produced vector-like quarks. An integrated luminosity corresponding to 35.9 fb${}^{\text{â}\text{ˆ}\text{’}1}$was recorded with the CMS experiment in 2016 at the LHC at $\sqrt{s}$= 13 TeV. The search is designed forvector-like quarks decaying into a W boson and a top quark with a muon or electron, hadronic jets, and missing transverse momentum in the final state. From the decay products, the invariant mass of the vector-like quark and the Standard Model background prediction, determined from control regions in data, are reconstructed. The event selection is optimised for the reconstructed invariant mass with simulation. Bottom quarks, boosted top quarks, as well as boosted W bosons reconstructed from hadronic decays and identified through algorithms, are exploited to increase the sensitivity of the search. No significant deviation from the background expectation of the Standard Model is observed, and exclusion limits at 95% confidence level are set for vector-like quark masses between 0.7 and 2 TeV. The exclusion limits on the product of the branching fraction and cross section range from 0.3 to 0.03 pb depending on the vector-like quark mass, the coupling, the relative width, and the type. Masses of up to 1660 GeV are excluded at a 95% confidence level for relative mass widths of 30%. The results of this analysis represent the most stringent results on single vector-like production, obtained in the tW channel.