Cosmogenic Background Characterization for the Colorado Underground Research Institute (CURIE)

Cosmic ray secondaries produced in Earth’s atmosphere present a dominant background in many experiments and equipment benchmarking efforts, especially for those requiring high levels of sensitivity to energy deposits. For such experiments and equipment testing, underground research facilities are an essential asset. These facilities are sought after due to the rock overburden, which provides natural protection from ionizing cosmogenic radiation, such as the near-elimination of cosmogenic muons. However, for many efforts such as dark matter searches or neutrinoless double beta decay experiments, the surviving cosmogenic muon and muon-induced events still present a significant background. One way to characterize and address these backgrounds, especially for R&D and equipment benchmarking, is to move to shallow underground facilities such as the new Colorado Underground Research Institute (CURIE). We present the characterization of cosmogenic muon and secondary backgrounds for CURIE located in the Edgar Experimental Mine in Idaho Springs, CO. The underground muon flux was simulated using the mute software package and subsequently validated with direct measurements, yielding a 700 fold reduction relative to the sea level surface muon flux. Additionally, a new depth-intensity relationship is proposed to interpret the overburden, which translates the muon attenuation to an equivalent overburden of ≈ 415 meter-water-equivalent (m.w.e.) for the fluxes observed at CURIE. Lastly, we discuss the muon-induced secondaries at the rock-cavern boundary which were simulated by coupling the underground muon angular and energy spectrum from mute with geant4.