Defining dark jets at the particle level

Sammanfattning: One hypothesis that attempts to explain dark matter is dark QCD, which suggests that there would be a dark sector made up of dark quarks. Dark quarks would interact with each other through dark QCD similar to how Standard Model quarks interact with each other through Standard Model QCD. Dark QCD would have several QCD-like features, one of which is dark jets. If dark quarks are produced at the LHC, they would produce dark jets, which could potentially have prompt or displaced decays into Standard Model jets, either fully or partially. However, there is currently no standardized definition of which jets should be considered dark. In this thesis, we will propose such a definition at particle level, and we will test the proposed definition on several dark QCD models. This definition is intended to be able to be used on a wide range of theoretical models, and can be refined to target specific models. We find that a suitable baseline definition of a dark jet is a jet for which at least 80\% of its pT originates from dark particles.