A Search for Quasi-Long-Lived Supersymmetric Particles within the CMS Detector at the LHC

This dissertation presents a search for supersymmetry (SUSY), an extension to the standard model (SM) of particle physics, with mass-degenerate co-next-to-lightest-stable particles (co-NLSP). These co-NLSP particles are sleptons: either a selectron or smuon. Both of these co-NLSP sleptons undergo decay to their standard model counterparts and a nearly massless gravitino. We analyze a dataset of 19.4 fb--1 collected during run one operations at the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider which ran at an 8 TeV center-of-mass collision energy. The co-NLSP sleptons in this model are quasistable, producing decays within the detector volume. We construct a custom analysis object composed of pairs of tracks that form a vertex at high precision.;Tracks in events that pass trigger cuts which use initial and final state radiation from the hard co-NLSP pair production process, as well as the missing transverse energy from the gravitino are candidates for inclusion in this custom analysis object. We impose a series of offline selection cuts designed to separate possible beyond SM decay signatures from mundane backgrounds such as quasielastic scattering or select standard model decays like charged kaon or sigma decay. We take tuples that pass these selection criterion and boost the putative daughter particle into the putative mother particle's reference frame to form a spectrum in p* which, under the assumption of a decay at a specified mass configuration, produces a delta distribution that is smeared via resolution effects into a signal shape originating from decay.;We observe at most three events in the data at the low end of our search region (100 GeV mother mass), which falls to zero events at a slepton mother mass of 260 GeV. These spectra are fit using a likelihood model with the signal probability density function being derived from simulation and the background selected as an exponential. Using Bayesian statistics and the profile likelihood technique we set limits on the co-NLSP slepton production cross section for masses between 100-210 GeV with proper lifetimes up to ctau = 93 cm.