Dark Matter Internal Pair Production -- A Novel Direct Detection Mechanism

We propose a novel mechanism, dark matter internal pair production (DIPP), to detect dark matter candidates at beam dump facilities. When energetic dark matter scatters in a material, it can create a lepton-antilepton pair by exchanging a virtual photon with the nucleus, similar to the neutrino trident process. We demonstrate this process for dark matter coupled to dark photons in experiments such as DarkQuest, SBND, and DUNE ND experiments. Since the pair-produced lepton-antilepton pair carries a large fraction of the center-of-mass energy and also has similar energy profiles, they can be clearly distinguished from backgrounds. We utilize the above features to show that DIPP is effective in probing various dark matter models, especially at DUNE ND and DarkQuest, by looking for electron-positron and muon-antimuon signatures. We also consider a scenario with dark sector couplings to quarks and muons only to show that DIPP can probe a wide range of dark matter models with various final states.