Resolving Quasi-Degenerate Higgs Bosons

Sammanfattning: Many models beyond the Standard Model that predict the existence of multiple Higgs bosons. In general, some of these additional Higgs bosons could be quasi-degenerate in mass either to each other or to the observed 125 GeV Higgs boson. The goal of this thesis is to study under which circumstances we can resolve such Higgs bosons. We first make the simplifying assumption that the observed and predicted invariant mass distributions are exact Gaussians, and use a $\chi^2$ test to determine how closely a combination of several particles resembles a single particle. We find that quasi-degenerate Higgs bosons with similar couplings are unlikely to be resolved by the experiments if their mass separation is less than twice the experimental resolution. We validate our findings by running Monte Carlo simulations of several important Higgs processes, and we find that the Gaussian approximation provides a decent description of when quasi-degenerate particles are resolvable. We finally consider interference effects in order to study cases where Higgs bosons have a much larger decay width than the Standard Model Higgs boson. We find that interference can make it significantly easier or significantly harder to resolve the two Higgs bosons, depending on the parameters of the model.