A CUPID Li₂¹⁰⁰MoO₄ scintillating bolometer tested in the CROSS underground facility

Abstract

A scintillating bolometer based on a large cubic Li 2 100 MoO 4 crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated in the CROSS cryogenic facility at the Canfranc underground laboratory in Spain. The dual-readout detector is a prototype of the technology that will be used in the next-generation 0 2 experiment CUPID. The measurements were performed at 18 and 12 mK temperature in a pulse tube dilution refrigerator. This setup utilizes the same technology as the CUORE cryostat that will host CUPID and so represents an accurate estimation of the expected performance. The Li 2 100 MoO 4 bolometer shows a high energy resolution of 6 keV FWHM at the 2615 keV line. The detection of scintillation light for each event triggered by the Li 2 100 MoO 4 bolometer allowed for a full separation (∼8) between () and events above 2 MeV. The Li 2 100 MoO 4 crystal also shows a high internal radiopurity with 228 Th and 226 Ra activities of less than 3 and 8 Bq/kg, respectively. Taking also into account the advantage of a more compact and massive detector array, which can be made of cubic-shaped crystals (compared to the cylindrical ones), this test demonstrates the great potential of cubic Li 2 100 MoO 4 scintillating bolometers for high-sensitivity searches for the 100 Mo 0 2 decay in CROSS and CUPID projects.

Optimization of the first CUPID detector module

“…We evaluated the baseline resolution as done for the LDs, with a result between 0.52 and 0.95 keV RMS depending on the LMO detector, with an overall average of (0.69 ± 0.06) keV RMS. The obtained performance is in agreement with previous cubic LMO detectors tested in the same facility [58] and consistent with cylindrical and cubic LMO detectors operated in similar conditions [49,56,60]. We evaluated the energy resolution at different energies by fitting the most intense γ peaks in the sum spectrum of the 8 LMO crystals (Fig.…”

“…Concerning the heat channel, a further improvement of the pulses amplitude estimation was possible through a thermal gain correction. Unlike the LDs, which exhibit typical resolutions of ∼1% [60], the heat channels are expected to reach a resolution of a few ∼0.1%.…”

“…CUPID-Mo operated at Laboratoire Souterrain de Modane (LSM) from early 2019 to mid 2020, proving the excellent radiopurity, energy resolution and α particles rejection achieved with cylindrical crystals of Li 2 100 MoO 4 (LMO), the compound chosen for CU-PID. The ongoing R&D measurements at the LNGS [58,59] and at the Canfranc laboratories [60] aim to optimize the detector features and design for the CUPID experiment. In this work we propose a new mechanical structure for the assembly of the CUPID baseline detector module and present its performance.…”

Background identification in cryogenic calorimeters through $$\alpha -\alpha $$ delayed coincidences

“…For example, in the analysis of CUORE data [30], delayed coincidences could help to better constrain the background sources [31] and to reject the time-correlated events falling in the region of interest. Moreover, the R&D activities for CUPID [32,33], CUPID-Mo [34][35][36], and in general the experiments searching for rare events can profit from this technique to study the radioactive contaminations of detector components and to select ultra-pure materials, with also the possibility to analyze other decay sequences in 238 U, 232 Th and 235 U chains [37]. Finally, the analysis of delayed coinci-dences in CUPID-0 allowed to measure the half-life of 216 Po [38].…”

CUORE Opens the Door to Tonne-scale Cryogenics Experiments

“…With the Li 100 2 MoO 4 technology well established, demonstrating an energy resolution of ∼5 keV FWHM [119] in the region of interest, ultra-low contamination levels (<3 𝜇Bq/kg both in thorium and uranium) and high reproducibility, the scintillating calorimeteric technique is ready to be expanded to a tonne-scale mass. Several activities are ongoing to finalize the detector design [126,127]. The CUORE cryostat is the natural choice to host the CUPID detector.…”