Dark Matter Induced Neutron Production Search Limits Using a Pb-Target*

Present WIMP Dark Matter (DM) search strategies are focused on possible direct detection through elastic or inelastic scatterings on atomic nuclei, or with electrons. This approach become insensitive to M(DM) < 10 GeV. Indirect DM detection refers to the search for DM-DM or DM-M annihilation, decay debris from DM particles, or other particle production, resulting in detectable species.

An indirect dark matter search was conduced using the 2002 NMDS-II cosmic ray muon-induced neutron data sets collected at the Center for Underground Physics in Pyhasalmi (CUPP). The data was collected at two depths, 583 m.w.e. collected for 6504 hours and for 1440 hours at 1166 m.w.e. The detector consists of a 30 cm cube Pb-target surrounded by 60 He-3 tubes. The He-3 detector system was found to have a neutron detection efficiency of 23.2 ± 1.2 when viewing Cf-252.

Limits on the hadronic cross section for DM-Pb interactions to produce neutrons are placed using the 1166 m.w.e data set containing 6 events by comparing to the larger data set at 583 m.w.e. considered to be produced by cosmic ray induced-neutron production and comparing independently with Geant4 simulations of cosmic ray-induced neutron production at both depths. Both comparisons indicate that no excess DM events were observed in the data set at 1166 m.w.e..

Two DM-Pb interaction neutron production models were used to estimate the DM detection efficiency, a proton-Pb spallation model and a pion fireball model. Both models are found to yield similar acceptances, to witnin 20% for DM-Pb interactions. Assuming no observed events, the 90% confidence limit search limits are 1× 10^(-44) cm^2 for 10 GeV deposited energy, 2×10^(−45) cm^2 for 1 GeV deposited energy and 3×10^(−45) cm^2 for 500 MeV deposited energy and no acceptance at 100 MeV.