Abstract
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 $\eta$ production can improve on the reach of LSND for light-mediator models with dark matter masses greater than $m_\pi/2$. 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.
Highlights
There is overwhelming gravitational evidence for the existence of dark matter (DM), its microscopic properties remain elusive despite decades of direct and indirect detection searches
High-intensity neutrino experiments remain an important component of the intensity frontier program, especially in their ability to discover or falsify models of DM which are invisible at traditional direct detection experiments
We have analyzed the capability of the JSNS2 experiment to probe two such models, where pseudo-Dirac DM has a mass splitting and interacts either through a dark photon or a dipole operator
Summary
There is overwhelming gravitational evidence for the existence of dark matter (DM), its microscopic properties remain elusive despite decades of direct and indirect detection searches (see Ref. [1] for a historical review). Beam dump experiments have emerged as powerful probes of DM below the GeV scale, thereby opening up a new frontier in the discovery effort In these experiments, a beam of protons [2,3,4,5,6] or electrons [7,8,9] impinges on a fixed target possibly yielding a secondary beam of DM particles that scatter or decay in a downstream detector; see Refs. The excellent reach of LSND is primarily due to the large detector mass and high beam power [∼3 × 1022 protons on target (POT)/year] [25], resulting in significant neutral pion creation (∼0.1 π0=POT), but many improvements are possible in future experimental programs. Further details of the matrix elements used in our reach projections are given in the Appendix
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