Unexpected Same-Charge Dilepton Signatures Resulting from Drell-Yan Events

Many theories, including several dark sector models, predict the existence of dark photons to explain dark matter as an extension beyond the Standard Model which interacts sparsely with Standard Model particles via kinetic mixing. The decay of dark photons is theorized to primarily decay into lepton jets that contain oppositely charged dileptons. In our Monte Carlo simulation, we see dilepton events through the Drell-Yan process, which generally produces oppositely charged lepton pairs and, provided their angle of separation is small, can appear as a lepton jet – therefore a prominent background for our dark photon search. However, we occasionally can see pairs of leptons with the same charge due to charge mismeasurement, among other reasons. These same- charge events occur at a vastly greater rate than expected. We investigate the rate as well as the cause of these same-charge dilepton events via our Monte Carlo. We do this by tracking the original particles that our dileptons came from in our generator- level Monte Carlo. Understanding our backgrounds is crucial to being able to perform a search.