Final result of CUPID-0 phase-I in the search for the ${}^{82}$Se Neutrinoless Double Beta Decay

Abstract

CUPID-0 is the first pilot experiment of CUPID, a next-generation project for the measurement of neutrinoless double beta decay (0$\hat{I}½$DBD) with scintillating bolometers. The detector, consisting of 24 enriched and 2 natural ZnSe crystals, has been taking data at Laboratori Nazionali del Gran Sasso from June 2017 to December 2018, collecting a ${}^{82}$Se exposure of 5.29 kg$\times$yr. In this paper we present the phase-I results in the search for 0$\hat{I}½$DBD. We demonstrate that the technology implemented by CUPID-0 allows us to reach the lowest background for calorimetric experiments: $(3.5_{-0.9}^{+1.0})\times 10^{-3}$ counts/(keV kg yr). Monitoring 3.88$\times$10${}^{25}$ ${}^{82}$Se nuclei$\times$yr we reach a 90% credible interval median sensitivity of ${\mathrm{T}}_{1/2}^{0\hat{\mathrm{I}}½}>5.0\times 10^{24}\mathrm{yr}$ and set the most stringent limit on the half-life of ${}^{82}$Se 0$\hat{I}½$DBD : ${\mathrm{T}}_{1/2}^{0\hat{\mathrm{I}}½}>3.5\times 10^{24}\mathrm{yr}$ (90% credible interval), corresponding to m${}_{{\hat{I}}^2{\hat{I}}^2}<$ (311-638) meV depending on the nuclear matrix element calculations.

6 pages, 3 figures