Search for Dark Photons Decaying to Lepton Jets: Prospects for CMS with HL-LHC

Production of dark photons with GeV-scale mass is predicted from models of supersymmetry and coupling of Higgs bosons to the dark sector. A distinctive signature is the presence of highly collimated jets of oppositely charged muons or electrons. We report the results of a simulation study of the CMS detector for p-p collisions at 14 TeV with average pile-up (interactions per bunch crossing) of 200. The efficiencies for detection of promptly produced dark photons and major Standard Model backgrounds are determined, and 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 the kinetic mixing parameter.