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Scintillation light generated as charged particles traverse large liquid argon detectors adds valuable information to studies of weakly-interacting particles. This paper uses both laboratory measurements and cosmic ray data from the Blanche dewar facility at Fermilab to characterize the efficiency of the photon detector technology developed at Indiana University for the single phase far detector of DUNE. The efficiency of this technology was found to be 0.48% at the readout end when the detector components were characterized with laboratory measurements. A second determination of the efficiency using cosmic ray tracks is in reasonable agreement with the laboratory determination. The agreement of these two efficiency determinations supports the result that minimum ionizing muons generate N phot = 40, 000 photons/MeV as they cross the LAr volume.

We (re)consider the sensitivity of past (LSND) and future (JSNS 2 ) beam dump neutrino experiments to two models of MeV-scale pseudo-Dirac dark matter. Both LSND and JSNS 2 are close (24-30 m) to intense sources of light neutral mesons which may decay to dark matter via interactions involving a light mediator or dipole operators. The dark matter can then scatter or decay inside of the nearby detector. We show that the higher beam energy of JSNS 2 and resulting η production can improve on the reach of LSND for light-mediator models with dark matter masses greater than mπ/2. Further, we find that both existing LSND and future JSNS 2 measurements can severely constrain the viable parameter space for a recently-proposed model of dipole dark matter which could explain the 3.5 keV excess reported in observations of stacked galaxy clusters and the Galactic Center.

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