Muon-induced background simulations for the Colorado Underground Research Institute

Muon-induced secondaries, particularly neutrons and high-energy photons, are an important source of background in underground facilities which require extremely low radiation environments. They can penetrate shielding and mimic signals in rare-event searches or interfere with the performance of sensitive quantum devices. Accurate characterization of these backgrounds is necessary both for designing low-background experiments and for optimizing research spaces that support technological development. We present a simulation study of muon-induced backgrounds for the Colorado Underground Research Institute (CURIE), a shallow site with approximately 415 meter-water-equivalent overburden. Using a two-stage approach that combines the MUTE transport framework with Geant4, we model the propagation of muons through site-specific geology and the production of secondary particles at laboratory depth. The study includes angular-dependent muon energy sampling to account for the effects of complex overburden anisotropy on underground fluxes. The framework produces results consistent with depth-dependent neutron flux parameterizations, giving confidence in its application to site-specific studies. Our work establishes a framework that couples fast and efficient transport calculations of the surface-to-depth muon flux with detailed particle interaction modelling at the rock–cavern boundary. This approach provides a flexible tool that can be adapted for end-to-end characterization of muon-induced backgrounds in shallow- and deep-underground facilities alike.