Enriched TeO2 bolometers with active particle discrimination: Towards the CUPID experiment

摘要

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 γ -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 μBq/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 μBq/kg for one crystal and 2.3 μBq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by β / γ particles by means of Neganov–Luke bolometric light detectors we were able to perform an event-by-event identification of β / γ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for α particles.