Search for dark photons decaying to lepton jets: Prospects for CMS Run III

Production of dark photons with GeV-scale mass is predicted in many dark sector models. A distinctive signature is the presence of two pairs of oppositely charged leptons (muons only, in this study) where the angle between the leptons in a pair is small but detectable. We report the results of preliminary studies for the sensitivity of the CMS experiment during Run III. The efficiencies for detection of promptly produced dark photons and major Standard Model backgrounds are determined. An event selection is developed that enhances the sensitivity of the search. The expected upper limit on the cross section is estimated and interpreted in terms of several production mechanisms.