Background model of the CUPID-0 experiment

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 scientific runs, CUPID-0 collected an exposure of 9.95 kg year. Thanks to the excellent rejection of \(\alpha \) particles, we attained the lowest background ever measured with thermal detectors in the energy region where we search for the signature of \(^{82}\hbox {Se}\) neutrinoless double beta decay. In this work we develop a model to reconstruct the CUPID-0 background over the whole energy range of experimental data. We identify the background sources exploiting their distinctive signatures and we assess their extremely low contribution [down to \(\sim 10^{-4}\) counts/(keV kg year)] in the region of interest for \(^{82}\hbox {Se}\) neutrinoless double beta decay search. This result represents a crucial step towards the comprehension of the background in experiments based on scintillating calorimeters and in next generation projects such as CUPID.