Dark Matter Internal Pair Production: A Novel Direct Detection Mechanism

We introduce a new dark matter detection 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, akin 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. Since the lepton-antilepton pair carries a significant fraction of dark matter energy, it can be clearly distinguished from backgrounds. Utilizing the above features, we show that DIPP is highly effective at probing various dark matter models, particularly at DUNE ND and DarkQuest, by searching for electron-positron and muon-antimuon signatures. At DUNE ND, we find that the sensitivity of DIPP extends over a larger parameter space than the existing limits from electron and nuclear recoil. Additionally, we explore a scenario where dark sector couplings involve quarks and muons only, demonstrating that DIPP can probe a wide variety of dark matter models with different final states.