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

We present the performances of two 92% enriched (TeO2)-Te-130 crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of Te-130. The crystals, 435 g each, show an energy resolution, evaluated at the 2615keV gamma-line of Tl-208, of 6.5 and 4.3keV FWHM. The only observable internal radioactive contamination arises from U-238 (15 and 8 mu Bq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, Ra-226 and Th-228, are both evaluated as < 3.1 mu Bq/kg for one crystal and < 2.3 mu Bq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by beta/gamma particles by means of Neganov-Luke bolometric light detectors we were able to perform an event-by-event identification of beta/gamma events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for alpha particles. (C) 2017 The Authors. Published by Elsevier B.V.