Search for supersymmetric partners of the top quark in models with compressed mass spectra with the CMS Detector

Supersymmetry (SUSY) is one of the most promising theories for physics beyond the standard model as it explains many of the current problems with the standard model of particlephysics (SM). For instance, in many minimal supersymmetric extensions of the SM the lightest supersymmetric particle (LSP) is a stable weakly interacting particle and is therefore anexcellent dark matter candidate. However, searches at Tevatron, LEP and the LHC havenot been able to find any signs of SUSY so far. This lack of indications for SUSY may beexplained if the LSP and the next-to-lightest SUSY particle have a small mass difference, ascenario which is referred to as compressed SUSY. In particular, SUSY scenarios with a lighttop squark (t) are well motivated since they allow for a natural mechanism to stabilize theloop corrections to the Higgs mass by partially cancelling the contributions coming from thetop quark. Additionally, the co-annihilation cross section between the LSP and a light topsquark can predict the dark matter relic density which is observed in the universe. This thesispresents a search for the pair production of the top squarks in SUSY models with compressedmass spectra using the 2016 proton-proton collision data collected at the CMS detector ofthe LHC. The single lepton channel of the four-body (t → bf f LSP) and chargino-mediated