Given the recent prominence of jets in many LHC analyses, modeling multijet backgrounds produced via QCD processes has become a prominent issue. Most physics-based simulations of QCD processes produce so few events in the signal phase space that statistical uncertainties become dominant. Even when not considering the simulated event yields, the phase space considered is often not modeled well by the physics simulation of these events. Presented in this dissertation is a robust solution to model these backgrounds with a data-driven method that simultaneously fits for simulation-based models of other backgrounds as well as Beyond Standard Model signals. The search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state is presented as a full example of an analysis using this novel background modeling method.
The analysis is performed using data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb-1 recorded by the CMS experiment at the LHC. The search is focused on heavy resonances, where the decay products of each top quark or W boson are expected to be reconstructed as a single, large-radius jet with a distinct substructure. The production of an excited bottom quark, b*, is used as a benchmark when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of b* quarks with left-handed, right-handed, and vector-like chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the b* quark mass to date, extending the previous best limits by almost a factor of two
