CURIE Site Information
Simulation and Measurement Validation
The Colorado Underground Research Institute (CURIE) utilized advanced Monte Carlo simulations (Daemonflux and MUTE) to accurately model the muon flux and depth, validated against direct experimental measurements. These simulations accounted for variations in rock composition and seasonal atmospheric shifts, ensuring accuracy in predicting muon behavior at shallow depths.
Site 0 and Site 1 measurements were conducted using stacked plastic scintillators to measure underground muon flux. These were consistent with simulations, validating the suitability of the CURIE facility for experiments needing moderate muon attention.
The table below is a summary of found fluxes and depths by each CURIE site.
Shielding Units at CURIE
CURIE provides exceptional shielding against cosmic ray muons, a primary source of background interference for surface-level experiments. Shielding is a critical factor for enabling low-background research, and CURIE’s infrastructure is tailored to meet the needs of various sensitive experiments.
CURIE’s shielding is quantified in terms of kilometer water equivalent (km.w.e), a standard metric that translates the overburden of rock into the equivalent thickness of water needed to achieve the same level of cosmic ray attenuation.
The shielding values at CURIE are:
- Depth: Approximately 200 meters of rock overburden above the lab sites
- Muon Flux Reduction: CURIE achieves a 700-fold reduction in cosmic ray muon flux compared to sea level
- Equivalent Depth: This corresponds to an effective shielding of 0.4 km.w.e., making CURIE comparable to other shallow underground facilities around the world
CURIE’s shielding values strike a critical balance between effectiveness and accessibility, providing researchers with a reliable environment to conduct sensitive experiments. The institute’s ability to mitigate cosmic ray muon flux by a factor of 700 positions it as a leading shallow underground facility, complementing deeper labs and advancing Mines’ commitment to cutting-edge scientific exploration.
Topological map of the 84 km2 area extracted from the USGS DEM data. The map is centered such that the entrance to the EEM is located at the origin of the plot. The z-axis is given in km above sea level.
Heatmap of the underground muon intensities as a function of arrival angle for Site 1. Note that the y-axis is given as an elevation angle for a more straightforward visual interpretation.
Muon Background Characterization and Attenuation
High-energy cosmic muons contribute significantly to background noise in physics experiments. To mitigate these effects, CURIE conducted comprehensive measurements of muon flux at Sites 0 and 1, finding that the Edgar Experimental Mine’s (EEM) location provides a 700-fold reduction in muon flux compared to sea level.
CURIE developed a new depth-intensity relationship to standardize the characterization of its overburden, allowing researchers to compare CURIE’s shallow depth with other underground facilities directly. This model integrates the impact of mountain overburden at CURIE to a standard “flat overburden” measure, enhancing the comparability with facilities globally.
(Left) The first iteration of the measurement setup to characterize the cosmic muon flux by coincidence in scintillation panels with varying inclines. (Middle, Right) Modeling of the angular dependence of the muon flux using LiDAR data from USGS and the DAEMONFLUX/MUTE simulation tools.