Enriched TeO${}_2$ bolometers with active particle discrimination: towards the CUPID experiment

Abstract

We present the performances of two 92% enriched ${}^{130}$TeO${}_2$ crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of ${}^{130}$Te. The crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV ${\hat{I}}^3$-line of ${}^{208}$Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from ${}^{238}$U (15 and 8 $\hat{I}¼$Bq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, ${}^{226}$Ra and ${}^{228}$Th, are both evaluated as $<$3.1 $\hat{I}¼$Bq/kg for one crystal and $<$2.3 $\hat{I}¼$Bq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by ${\hat{I}}^2/{\hat{I}}^3$ particles by means of Neganov-Luke bolometric light detectors we were able to perform an event-by-event identification of ${\hat{I}}^2/{\hat{I}}^3$ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for $\hat{I}\pm$ particles.