Dark Photon Search at Yemilab, Korea

Abstract: Dark photons are well motivated hypothetical dark sector particles that could account for observations that cannot be explained by the standard model of particle physics. A search for dark photons that are produced by an electron beam striking a thick tungsten target and subsequently interact in a 3 kiloton-scale neutrino detector in Yemilab, a new underground lab in Korea, is proposed. Dark photons can be produced by "darkstrahlung" or by oscillations from ordinary photons produced in the target and detected by their visible decays, "absorption" or by their oscillation to ordinary photons. By detecting the absorption process or the oscillation-produced photons, a world's best sensitivity for measurements of the dark-photon kinetic mixing parameter of $\epsilon^2 > 1.5 \times 10^{-13} (6.1 \times 10^{-13})$ at the 95\% confidence level (C.L.) could be obtained for dark photon masses between 80 eV and 1 MeV in a year-long exposure to a 100 MeV-100 kW electron beam with zero ($10^3$) background events. In parallel, the detection of $e^+e^-$ pairs from decays of dark photons with mass between 1 MeV and $\sim$86 MeV would have sensitivities of $\epsilon^2 > \mathcal{O}(10^{-17}) (\mathcal{O}(10^{-16}))$ at the 95% C.L. with zero ($10^3$) background events.