Search for Stealth Supersymmetry in Proton-Proton Collisions with the CMS Experiment at the Large Hadron Collider

This Thesis documents a search for Stealth supersymmetry (SUSY) in final states with two photons, jets, and low missing transverse momentum. Over the data-taking period of the LHC, a progressively larger fraction of the well-motivated parameter-space for typical SUSY models has been ruled out experimentally, but these signal models typically assume a signature with high missing transverse momentum. The study documented here helps close the gap by extending the search to a specific subset of SUSY models called "Stealth SUSY" that do not have this signature, but happen to be nearly as phenomenologically well-motivated as typical minimal supersymmetric Standard Model scenarios. An innovative "hybrid" approach is used to estimate the background, which involves the augmentation of a zeroth-order data-driven background model with first-order corrections obtained from Monte Carlo simulations of the background. The search is based on a 138 fb$^{-1}$ sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector. The results are interpreted in the context of simplified stealth models with gluino and squark pair production. The observed data are consistent with the Standard Model prediction, and gluino (squark) masses of up to 2.1 (1.85) TeV are excluded.