Limits on Excess Neutron Number Production in a Pb-Target at 583 m.w.e. Underground*

     New physics processes, initiated by cosmic rays or though dark matter interactions may be observable by excess neutron number production within the neutron number spectrum measured using high-A nuclear targets.  For this purpose, data has been collected and analyzed using the NMDS-II detector located at a depth of 220 m below sea-level, or 583 m.w.e. at the Center for Underground Physics in Pyhasalmi, CUPP, in Finland. The detector consists of a 30 cm, 305kg cubic lead target, instrumented with 60, He-3 neutron counters and a two-layer Geiger Counter system for the detection of muons.     

     The data consists of two distinct triggers; The first demands the presence of a muon and a minimum of 4 observed neutrons having a live time of 4793 hours. The second requires a minimum of 4 neutrons in this analysis, having a live time of 6504 hours. The neutron number spectrum for both trigger types is presented and these two data sets are compared to GEANT4 calculations to set limits on possible excess neutron number production in the neutron nunber spectrum for both sets of events types, with and without a muon passing through the Pb-target.

     To set the energy scale and the integrated flux, a single ~10 TeV muon is expected to pass through the detector in the collected data sets and GEANT4 predicts events producing  ~250 neutrons to be observed.