Simulation of muon-induced backgrounds for the Colorado Underground Research Institute

We present a comprehensive Monte Carlo simulation of muon-induced backgrounds for the Colorado Underground Research Institute, a shallow-underground facility with ≈ 415 meter water equivalent overburden. Using coupled and 4 frameworks, we characterize the production and transport of muon-induced secondaries through site-specific rock compositions and geometries, establishing a proof of concept for high-precision, end-to-end simulations. Our simulations employ angular-dependent muon energy distributions, which improve secondary flux accuracy. For the Subatomic Particle Hideout and Cryolab I research spaces, we predict total muon-induced neutron fluxes of ( 8.52 ± 1.3 0 sys ) × 10 − 3 m − 2 s − 1 and ( 8.86 ± 1.6 2 sys ) × 10 − 3 m − 2 s − 1 , respectively. Electromagnetic backgrounds are expected to dominate the total flux, with γ -ray components of ( 5.54 ± 0.7 0 sys ) × 10 − 1 m − 2 s − 1 and ( 6.51 ± 1.0 6 sys ) × 10 − 1 m − 2 s − 1 for the Subatomic Particle Hideout and Cryolab I facilities, respectively. Additionally, we develop a depth-intensity relation to predict the muon-induced neutron flux as a function of facility depth, which is consistent with measurements across a broad range of underground depths. These results provide quantitative background predictions for experimental design and sensitivity projections at shallow- and deep-underground facilities. They further demonstrate that local geology and overburden geometry influence muon-induced secondary yields and energy spectra, emphasizing the need for site-specific simulations for accurate underground background characterization. Therefore, the simulation framework has been made pu