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$^{ 0\nu}_{ 1/2}$($^{ 82}$Se)$>$ 4.6$\times \mathrm{ 10}^{ 24}$ yr (90\% credible interval), corresponding to an effective Majorana neutrino mass m$_{ \beta\beta} <$ (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.
Categories: hep-ex nucl-ex physics.ins-det