Heavy resonance hunting at the LHC

Abstract

The need for new physics beyond the Standard Model is apparent given all the evi- dence collected in experiments throughout the last decades. Many new physics mod- els, that try to explain the deviations from the Standard Model, predict heavy particles that are accessible at the Large Hadron Collider (LHC). Although there are different ways to discover new particles, resonance searches belong to one of the most powerful types of analyses. In this dissertation, we will present various aspects of resonance searches and how they can be used to constrain physics beyond the Standard Model. By recasting an existing LHC search we determine limits on a lepton flavour violat- ing two Higgs doublet model. For a quark flavour violating two Higgs doublet model we develop a new superior analysis for a top plus two Higgs final state and compare the results to existing and projected limits. In some circumstances the pair production channel of a new heavy state provides a model-independent way to test the particle’s existence, whereas the single resonance production mode would be model-dependent. This is the case for a massive coloured octet vector. We design a search dedicated to find such a pair produced resonance if neither a subsequent decay to top quarks nor to lighter quarks dominates. Furthermore, we determine the prospects of spin discrimination for a heavy reso- nance decaying to two massive bosons. We study the implications of jet substructure techniques on angular correlations that are vital for such a discrimination. Using a fully hadronic final state we determine the projected reach at the LHC. Occasionally, a resonance cannot be seen directly since the final state particles may be dark matter. We use a displaced and prompt lepton jet analysis to study how effects of a parton shower in the dark sector can yield information about the underlying physics. We also provide a semi-analytic description of such a dark shower.