Searching for Dark Photons with Jet

Sammanfattning: Dark matter is the greatest mystery of modern particle physics and cosmology. Although an overwhelming amount of observational cosmological evidence has pointed towards a dark sector, only its gravitational effect has been experimentally confirmed. Currently, no other properties of dark matter are known, including its mass, interactions else than gravitational and potential mediators between dark matter and the particles of the Standard Model. In recent time, the idea of probing dark matter in the sub-GeV mass region with an electromagnetic coupling has become increasingly popular. In this paper, a simplified light dark matter model is adapted as a toy model. We investigate lepton jets as a promising signature for the U(1)_D dark photon mediator $A'$, using an off-the-shelf search strategy widely used by experimentalists at the Large Hadron Collider. At this collider, the O(GeV) dark boson decays into a pair of leptons, which further go on to creating a leptonic jet signature. The thesis is begun by a study of the dark photon decay kinematics using truth distributions. The kinematical study looks for effective methods to distinguish signal from background by observing the characteristic energy, spatial and momentum distributions of signal leptons. This is followed by a jet substructure analysis including jet filtering, mass drop tagging and sub-jet correlations, where we conclude that the applied off-the-shelf analysis is not as efficient in isolating the dark photon signal as originally considered.