Final Result on the Neutrinoless Double Beta Decay of ${}^{82}$Se with CUPID-0

Abstract

CUPID-0, an array of Zn${}^{82}$Se cryogenic calorimeters, was the first medium-scale demonstrator of the scintillating bolometers technology. The first project phase (March 2017 - December 2018) allowed the most stringent limit on the neutrinoless double beta decay half-life of the isotope of interest, ${}^{82}$Se, to be set. After a six months long detector upgrade, CUPID-0 began its second and last phase (June 2019 - February 2020). In this letter, we describe the search for neutrinoless double beta decay of ${}^{82}$Se with a total exposure (phase I + II) of 8.82 kg$\times$yr of isotope. We set a limit on the half-life of ${}^{82}$Se to the ground state of ${}^{82}$Kr of T${}_{1/2}^{0\hat{I}½}$(${}^{82}$Se)$>$ 4.6$\times {10}^{24}$ yr (90\% credible interval), corresponding to an effective Majorana neutrino mass m${}_{{\hat{I}}^2{\hat{I}}^2}<$ (263 -- 545) meV. We also set the most stringent lower limits on the neutrinoless decays of ${}^{82}$Se to the 0${}_1^{+}$, 2${}_1^{+}$ and 2${}_2^{+}$ excited states of ${}^{82}$Kr, finding 1.8$\times$10${}^{23}$ yr, 3.0$\times$10${}^{23}$ yr, 3.2$\times$10${}^{23}$ yr (90$\%$ credible interval) respectively.