Search

CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) is a project aiming to develop a new bolometric technology enabling an active background rejection in 0v2β search. The isotopes of interest are 100Mo and 130Te, and bolometers are based on Li2MoO4 and TeO2 crystals. The key feature of CROSS detectors is the possibility of pulseshape discrimination of near surface interactions. An ultrapure superconductive aluminum film, deposited on the crystal surface, is acting as a pulse-shape modifier for phonon sensors, providing separation of surface events from bulk ones. First prototypes were produced and successfully tested aboveground with the rejection of α surface radioactivity higher than 99.9%. A demonstrator with 32 0.28-kg Li2 100MoO4 crystals will be installed in a dedicated cryostat in the Canfranc underground laboratory (Spain) to confirm the reproducibility of surface sensitive bolometers. CROSS demonstrator can obtain sensitivities to the effective Majorana mass down to 70 meV in the most favorable conditions. The CROSS technology can be applied for future ton-scale experiments, reaching sensitivities to the effective Majorana mass down to 10 meV.

We have developed a contact-less technique for the real time measurement of a-thermal (Cooper-pair breaking) phonons in an absorber held at sub-Kelvin temperatures. In particular, a thin-film aluminum superconducting resonator was realized on a 30-grams high-resistivity silicon crystal. The lumped-element resonator is inductively excited/read-out by a radio-frequency microstrip feed-line deposited on another wafer; the sensor, a Kinetic Inductance Detector (KID), is read-out without any physical contact or wiring to the absorber. The resonator demonstrates excellent electrical properties, particularly in terms of its internal quality factor. The detection of alphas and gammas in the massive absorber is achieved, with an RMS energy resolution of about 1.4 keV, which is already interesting for particle physics applications. The resolution of this prototype detector is mainly limited by the low (about 0.3%) conversion efficiency of deposited energy to superconducting excitations (quasi-particles). The demonstrated technique can be further optimized, and used to produce large arrays of a-thermal phonon detectors, for use in rare events searches such as: dark matter direct detection,neutrino-less double beta decay, or coherent elastic neutrino-nucleus scattering., Accepted for publication on Applied Physics Letters