We report the result of the search for neutrinoless double beta decay of ${}^{82}\mathrm{Se}$ obtained with CUPID-0, the first large array of scintillating $\mathrm{Zn}{}^{82}\mathrm{Se}$ cryogenic calorimeters implementing particle identification. We observe no signal in a 1.83 kg yr ${}^{82}\mathrm{Se}$ exposure, and we set the most stringent lower limit on the $0\nu \beta \beta$ ${}^{82}\mathrm{Se}$ half-life $T_{1/2}^{0\nu }>2.4\times {10}^{24}\mathrm{yr}$ (90% credible interval), which corresponds to an effective Majorana neutrino mass $m_{\beta \beta }<(376–770)\mathrm{meV}$ depending on the nuclear matrix element calculations. The heat-light readout provides a powerful tool for the rejection of $\alpha$ particles and allows us to suppress the background in the region of interest down to $({3.6}_{-1.4}^{+1.9})\times {10}^{-3}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, an unprecedented level for this technique.

CUPID-0 is the first pilot experiment of CUPID, a next-generation project for the measurement of neutrinoless double beta decay ($0\nu \mathrm{DBD}$) 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 ${}^{82}\mathrm{Se}$ exposure of $5.29\mathrm{kg}\times \mathrm{yr}$. In this Letter we present the phase-I results in the search for $0\nu \mathrm{DBD}$. We demonstrate that the technology implemented by CUPID-0 allows us to reach the lowest background for calorimetric experiments: $({3.5}_{-0.9}^{+1.0})\times {10}^{-3}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$. Monitoring $3.88\times {10}^{25}$ ${}^{82}\mathrm{Se}$ $\mathrm{nuclei}\times \mathrm{yr}$ we reach a 90% credible interval median sensitivity of $T_{1/2}^{0\nu }>5.0\times {10}^{24}\mathrm{yr}$ and set the most stringent limit on the half-life of ${}^{82}\mathrm{Se}$ $0\nu \mathrm{DBD}$: $T_{1/2}^{0\nu }>3.5\times {10}^{24}\mathrm{yr}$ (90% credible interval), corresponding to ${\mathrm{m}}_{\beta \beta }<(311–638)\mathrm{meV}$ depending on the nuclear matrix element calculations.

The CUPID-0 detector hosted at the Laboratori Nazionali del Gran Sasso, Italy, is the first large array of enriched scintillating cryogenic detectors for t

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

The suppression of spurious events in the region of interest for neutrinoless double beta decay will play a major role in next generation experiments. The