Prospective study of light dark matter search with a newly proposed DarkSHINE experiment

Dark photons have been well motivated as strong candidates for dark force carriers and light dark matter in the sub-GeV mass range. Compared with collider experiments, fixed-target experiments provide a complementary approach to searching for dark photons, particularly in the lower mass range. We have studied the physics potential of the electron-on-target experiment based on the Shanghai SHINE facility, which provides 10 MHz single electron beam at 8 GeV energy. This analysis focuses on dark photons being produced via electron and nucleon interaction and then decays to dark matter candidates, which escape detection as missing momentum in the detector. This experiment takes advantage of using missing momentum to enhance signal versus background separation power. In this study, signal samples as a function of dark photon mass and an inclusive background sample with 2.5 billion events are simulated with GEANT4. For better background estimates, major rare background processes have also been simulated. This paper presents the experiment and detector design, signal and background simulations, analysis strategy, and the prospective study of the experiment sensitivity. With 9 × 10 14 electron-on-target events (about three years running), this experiment is expected to rule out most of the sensitive regions predicted by popular dark photon models.