First characterization of the ultra-shielded chamber in the low-noise underground laboratory (LSBB) of Rustrel-Pays dʹApt

In compliance with international agreements on nuclear weapons limitation, the French ground-based nuclear arsenal has been decommissioned in its totality. One of its former underground missile control centers, located in Rustrel, 60 km east of Avignon (Provence) has been converted into the “Laboratoire Souterrain à Bas Bruit de Rustrel-Pays dʹApt” (LSBB). The deepest experimental hall (500 m of calcite rock overburden) includes a 100 m2 area of sturdy flooring suspended by and resting on shock absorbers, entirely enclosed in a 28 m long, 8 m diameter, 1 cm thick steel capsule. This results in an unparalleled combination of shielding against cosmic rays, acoustic, seismic and electromagnetic noise, which can be exploited for rare event searches using ultra low-temperature and superconducting detectors. The first characterization measurements in this unique civilian site are reported.