UC Davis

This dissertation details the context and methods involved in the analysis conducted to searchfor excited tau leptons (τ∗) using data collected during Run II of the Large Hadron Collider (LHC) by the Compact Muon Solenoid (CMS) experiment. The dataset used corresponds to 138 fb−1 of integrated luminosity in proton-proton collisions at 13 TeV center-of-mass energy. The analysis selects events with two tau candidates, at least one of which is a hadronic decay, and a high energy photon. The mass of the excited tau lepton is reconstructed by also accounting for the contribution from the invisible neutrino component. Expected limits are set at 95% confidence level excluding mτ∗ up to 4.5 TeV for a compositeness scale equal to the mass of the τ∗ and up to 2.75 TeV for a compositeness scale of 10 TeV.