Search

International audience; BULLKID is an R&D project on a cryogenic particle detector to search for rare low-energy processes such as low-mass dark matter and neutrino coherent scattering off nuclei. The detector unit we are designing consists in an array of ~ 100 silicon absorbers sensed by phonon-mediated, microwave-multiplexed kinetic inductance detectors, with energy threshold below 100 eV and total target mass around 30 g. The single detector unit will be engineered to ensure a straightforward scalability to a future kg-scale experiment.

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.

International audience; Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei $^{100}$Mo and $^{130}$Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of α surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li$_{2}$MoO$_{4}$ and TeO$_{2}$. We have also shown that point-like energy depositions can be identified up to a distance of ∼ 1 mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising ∼ 3×10$^{25}$ nuclei of $^{100}$Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.[graphic not available: see fulltext]

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