Hiltbrand, Joshua2022-09-262022-09-262022-07https://hdl.handle.net/11299/241741University of Minnesota Ph.D. dissertation. July 2022. Major: Physics. Advisor: Nadja Strobbe. 1 computer file (PDF); vi, 166 pages.Searches for top squark decays within R-parity violating and Stealth SYY supersymmetry models are presented. Motivation is given for extending the standard model with an additional supersymmetry and why the aforementioned models are relevant to search for at the LHC with the CMS experiment. Final results of a first-of-its-kind search are presented where the detector signature is many jets and a lepton. Data collected from 2016 to 2018 during LHC’s Run2 campaign are analyzed, totaling 138 fb−1. A preference for signal with a local significance of 2.8σ is observed when assuming a top squark mass of 400 GeV and the R-parity violating model. Based on this result, another search is actively being developed to also look for the signature of many jets with no lepton. Novel machine learning techniques are used to automate the background estimation strategy. The projected sensitivity of the new analysis is summarized.enThesis or Dissertation