Abstract
CUPID-0 is the first large mass array of enriched Zn^{82}Se scintillating low temperature calorimeters, operated at LNGS since 2017. During its first scientific runs, CUPID-0 collected an exposure of 9.95 kg year. Thanks to the excellent rejection of alpha particles, we attained the lowest background ever measured with thermal detectors in the energy region where we search for the signature of ^{82}hbox {Se} neutrinoless double beta decay. In this work we develop a model to reconstruct the CUPID-0 background over the whole energy range of experimental data. We identify the background sources exploiting their distinctive signatures and we assess their extremely low contribution [down to sim 10^{-4} counts/(keV kg year)] in the region of interest for ^{82}hbox {Se} neutrinoless double beta decay search. This result represents a crucial step towards the comprehension of the background in experiments based on scintillating calorimeters and in next generation projects such as CUPID.
Highlights
The postulated neutrinoless double beta decay (0νββ) consists of two neutrons of an atomic nucleus simultaneously decaying to two protons and two electrons, without the accompanying emission of electron antineutrinos [1]
The radioactive decays from the various background sources can be generated in any volume or surface of the CUPID-0 detector, cryostat and shielding implemented in Arby
We identify the contribution of the various background sources to the ROIbkg counting rate and we perform an analysis of the corresponding systematic uncertainties
Summary
The postulated neutrinoless double beta decay (0νββ) consists of two neutrons of an atomic nucleus simultaneously decaying to two protons and two electrons, without the accompanying emission of electron antineutrinos [1]. The experimental signature of 0νββ is a peak at the end of the continuous spectrum produced by the electrons emitted in two-neutrino double beta decay, an allowed, extremely rare, second order nuclear transition. Detectors with excellent energy resolution, such as low temperature calorimeters (historically called bolometers), are the best candidates to study this process, being able to disentangle the searched peak from the continuous background. 2), we analyze the experimental spectra in wide energy ranges, from a few hundred keV to ∼ 10 MeV, to find signatures of background sources The energy spectra produced in the detector by each source are simulated by means of a Monte Carlo code 6), we present the fit results, i.e. the activities obtained for the background sources and their contribution to the 0νββ ROI, as well as a discussion of systematic uncertainties (Sect. 6), we present the fit results, i.e. the activities obtained for the background sources and their contribution to the 0νββ ROI, as well as a discussion of systematic uncertainties
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