The Search for a Heavy Top-Like Quark

The Standard Model (SM) has stood as one of the cornerstones of modern physics for the past 40 years; yet it is likely to remain only as an eective eld theory. In particular, new beyond the SM theories are required to explain both the baryon-antibaryon asymmetry observed in the Universe and the unnatural lightness of the tentatively observed Higgs boson. Such theories often predict heavy partners to the six observed quarks, which naturally explain these phenomena. In this thesis, we present two searches for a heavy top-like quark at the LHC using data collected by the CMS detector. In 2011, we searched for a sequential fourth generation t 0 using 5 fb 1 of data at a p s = 7 TeV centre of mass energy [ 1 ]. In 2012, we searched for a vector-like T that partners the SM top quark using 19 : 6 fb 1 of data at p s = 8 TeV [ 2 , 3 ]. In both analyses, we used a semileptonic event topology, consisting of events with exactly one lepton. No excess over SM predictions are observed and the heavy top-like quark is ruled out below the mass of 700 GeV/ c 2 across the entire phase space. This is the rst analysis of its kind and we set the most stringent limit on this entire class of beyond the SM theories to date