# Background Model of the CUPID-0 Experiment

## TL;DR

This paper develops a detailed background model for the CUPID-0 experiment, achieving the lowest background levels in the search for neutrinoless double beta decay, which is vital for future low-background experiments.

## Contribution

It introduces a comprehensive background reconstruction model for CUPID-0, identifying and quantifying background sources across the entire energy spectrum.

## Key findings

- Achieved background levels as low as ~10^{-4} counts/(keV kg yr) in the ROI.
- Successfully identified and characterized background sources.
- Demonstrated the model's importance for future scintillating calorimeter experiments.

## Abstract

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 yr. 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 $^{82}$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 $\sim10^{-4}$ counts/(keV kg yr)) in the region of interest for $^{82}$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.