CUPID-0, challenges and achievements in the struggle of 0-background double-beta decay experiments

The background is the key issue of any experiment searching for the neutrinoless double beta decay (0νDBD) and one of the possible solutions is the use of high resolution detectors in which background can be actively discriminated. CUPID-0 is the first 0νDBD experiment based on scintillating bolometers able to perform efficient particle identification allowing for background reduction at the unprecedented level of ∼10−3 cts/(keV⋅kg⋅yr). This work makes an overview of the main problems and solutions applied in the construction of the CUPID-0 experimental apparatus, starting from the production of the crystal up to the assembly of the detector. Particular attention is payed to the methods applied to avoid the radio-contamination. The recovery of enriched Se loss along the crystal production cycle is discussed as the main challenge for the budget of this kind of experiments. The good bolometric performance of crystals is emphasized together with supplementary discrimination power offered in the case of ZnSe by the pulse shape analysis, besides the bare scintillation signal. We also make a brief report on detector performance and the results obtained till present which allowed us to establish the world best half-time limit on 82Se 0νDBD of >2.4⋅ 1024 yr (90% C.I.).