A CUPID Li${}_2$${}^{100}$MoO${}_4$ scintillating bolometer tested in the CROSS underground facility

Abstract

A scintillating bolometer based on a large cubic Li${}_2$${}^{100}$MoO${}_4$ crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated in the CROSS cryogenic facility at the Canfranc underground laboratory in Spain. The dual-readout detector is a prototype of the technology that will be used in the next-generation $0\nu 2{\hat{I}}^2$ experiment CUPID. The measurements were performed at 18 and 12 mK temperature in a pulse tube dilution refrigerator. This setup utilizes the same technology as the CUORE cryostat that will host CUPID and so represents an accurate estimation of the expected performance. The Li${}_2$${}^{100}$MoO${}_4$ bolometer shows a high energy resolution of 6 keV FWHM at the 2615 keV ${\hat{I}}^3$ line. The detection of scintillation light for each event triggered by the Li${}_2$${}^{100}$MoO${}_4$ bolometer allowed for a full separation ($\sim$8$\ddot{I}ƒ$) between ${\hat{I}}^3$(${\hat{I}}^2$) and $\hat{I}\pm$ events above 2 MeV. The Li${}_2$${}^{100}$MoO${}_4$ crystal also shows a high internal radiopurity with ${}^{228}$Th and ${}^{226}$Ra activities of less than 3 and 8 $\hat{I}¼$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 $0\nu 2{\hat{I}}^2$ decay in CROSS and CUPID projects.

19 pages, 7 figures, 1 table