Characterisation of the Bedretto Underground Site for Fundamental Physics Experiments

TL;DR

This study thoroughly characterizes the Bedretto underground site in Switzerland, demonstrating its suitability for advanced physics experiments due to its low background noise, radiation levels, and excellent infrastructure.

Contribution

It provides the first comprehensive environmental assessment of the Bedretto site, highlighting its potential as Europe's second-deepest, quietest underground laboratory for fundamental physics.

Findings

Muon flux suppressed by six orders of magnitude

Low gamma-ray and neutron backgrounds consistent with local geology

Exceptional magnetic and seismic noise levels

Abstract

Underground laboratories provide the ultra-low background and low-vibration environments essential for rare-event searches, gravitational-wave detection, and quantum-sensing technologies. We report a comprehensive environmental characterisation of the Bedretto tunnel in Ticino, Switzerland, a site offering horizontal access, excellent infrastructure, and the potential to be be Europe's second-deepest and quietest underground laboratory. At the prospective physics site, located beneath an overburden exceeding 1400 m, we measure the cosmic-muon, gamma-ray, and neutron fluxes, as well as the radon concentration, magnetic-field spectrum, and seismic backgrounds. The muon flux is suppressed by six orders of magnitude relative to the surface, consistent with an effective depth of about 4000 metre water equivalent, gamma-ray and neutron measurements reflect the local geology and guide shielding requirements for future particle and nuclear physics experiments. Magnetic and seismic noise levels are found to be exceptionally low, meeting or exceeding the criteria for next-generation atom-interferometric gravitational-wave detectors. These results establish the site as a highly competitive, accessible deep-underground location for fundamental-physics experiments.