Search for Heavy Top Quark Partners with Charge 5/3 and Anomalous Higgs $(→b\overline{b})$ Couplings to Vector Bosons

In this thesis, we present two searches for new physics performed using the data collected by the CMS experiment at the LHC at two different center of mass energies. In the first part, we present a search for anomalous Higgs couplings. In 2012, the ATLAS and CMS experiments at the LHC discovered a new boson. This discovery completed a long search for the final missing piece of the standard model (SM). The measurements so far confirm that the new boson is consistent with the Higgs boson predicted by the SM. However, there are decay channels that are yet to be confirmed experimentally; e.g., the decay to a pair of bottom quarks. In addition, precision measurements of the Higgs couplings to all SM particles need to be performed in order to make sure there is no deviation from the predictions of the SM. We present the first search at the LHC for anomalous couplings of the Higgs boson H to vector bosons V (= W or Z) using associated Higgs production with the Higgs boson decaying to a pair of bottom quarks. We use the data collected with the CMS detector from proton-proton collisions in 2012 at a center of mass energy of 8 TeV. Even though the exclusion limit derived from this production channel alone is at the 68% CL using the 2012 data, we demonstrate the power of this channel in constraining very small anomalous Higgs couplings to vector bosons. Combining the results from this channel with the previously published H → VV channels, we put more stringent constraints on anomalous Higgs couplings to vector bosons. The second part of the thesis deals with the so called hierarchy problem, caused by quadratically divergent radiative corrections to the Higgs mass at higher energy scales. The corrections are many orders of magnitude larger than the observed mass and it requires unnatural fine-tuning to cancel out these contributions. There are different models that attempt to address this problem, one of which is the Composite Higgs Model that predicts a very heavy fermionic partner of the top quark with an electric charge of 5/3 (X$_{5/3}$). X$_{5/3}$ decays into a W boson and a top quark, which then decays into a bottom quark and a W boson. We analyze the events in which one of the W bosons in the X$_{5/3}$ pair production final state decays into leptons and the remaining three W’s decay hadronically. We present here the first study of X$_{5/3}$ at the LHC in the lepton + jets decay channel using events from the data collected in 2015 with the CMS detector at a center of mass energy of 13 TeV in Run 2 of the LHC. The results are also combined with the more sensitive same-sign dilepton channel.