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 $\gamma$-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 $\mu$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 $\mu$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.
Highlights
The following three important questions in neutrino physics will be addressed by generation neutrinoless double beta decay (0ν-DBD) experiments: are neutrinos Majorana particles that differ from antineutrinos only by helicity? Is lepton number conservation violated? What is the neutrino mass-scale? Searches for0ν-DBD have been carried out for many decades investigating a large variety of nuclei with many different experimental techniques [1]
The initial idea to decrease the α-background in DBD bolometers was to use scintillating crystals [12] in which the discrimination between e/γ and α/neutron particles can be obtained with the additional readout of the scintillation light, through a second – very sensitive – bolometer working as a Light Detector (LD)
The LDs developed for DBD scintillating bolometers experiments [25] generally consist of Ge wafers coupled to Neutron Transmutation Doped (NTD) Ge thermistors
Summary
The following three important questions in neutrino physics will be addressed by generation neutrinoless double beta decay (0ν-DBD) experiments: are neutrinos Majorana particles that differ from antineutrinos only by helicity? Is lepton number conservation violated? What is the neutrino mass-scale? Searches for. The goal of the generation 0ν-DBD experiments is to sensitively probe the entire inverted hierarchy region. To reach this sensitivity, the total masses of parent isotopes must be increased using enriched isotopes, and the backgrounds drastically decreased. The advantage of the bolometric technique proposed for CUPID is the possibility to choose different DBD emitters combined with the capability of having a high resolution detector, but the realization of double-readout detectors in order to perform an active particle discrimination to reject the natural background. The initial idea to decrease the α-background in DBD bolometers was to use scintillating crystals [12] in which the discrimination between e/γ and α/neutron particles can be obtained with the additional readout of the scintillation light, through a second – very sensitive – bolometer working as a Light Detector (LD). This work demonstrates that 130TeO2 can be a suitable candidate for the CUPID experiment in terms of energy resolution, internal radioactive contaminations and α-background discrimination
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