Dark Matter Induced Neutron Production Search Limits

An independent indirect detection search for Dark Matter-Matter (DM-M) interactions is undertaken to set cross section limits based on neutron production data collected by the NMDS-II detector for 1440 hours at 1166 m.w.e. and 6504 hours at 583 m.w.e.. The detector system consists of a 30 cm cube Pb-target instrumented with 60 $^3$He neutron counters. The neutron detector system calibrated with a $^{252}$Cf source yields a single particle detection efficiency of 23.2\%$\pm$1.2\%. During data collection, the highest neutron multiplicity event observed 54 neutrons. The neutron multiplicity, n, distribution, fits well to a power law $k \times n^{-p}$, for both the data and cosmic ray muon induced neutron production in Geant4 simulations. Two DM-M interaction models were used to set limits. The first, a spallation model, assumes a single proton with kinetic energy equal to the DM-M interaction energy. The other, a fire-ball model assumes an annihilation between DM-M producing pions with a limiting Hagedorn temperature. The two extreme models produce similar upper DM-M cross section limits over the DM mass range between 300 MeV to 100 GeV. Limits assume all the DM energy is deposited in the Pb-target. Spin independent limits, proportional to A$^{-2}$, are at the level ~10$^{-45}~ cm^2$. Spin dependent limits, proportional to A$^{-1}$, are at the level, $2\times 10^{-42}~cm^2$.