# Characterization of Light Production and Transport in Tellurium Dioxide Crystals

## TL;DR

This paper provides detailed measurements and modeling of light production and transport in tellurium dioxide crystals, crucial for optimizing particle detection in neutrinoless double-beta decay experiments.

## Contribution

It offers the first comprehensive optical characterization of TeO$_2$ crystals, including surface properties and scintillation limits, aiding the development of high-sensitivity light detectors for CUPID.

## Key findings

- Quantitative light production and transport data for TeO$_2$ crystals.
- Limits on room-temperature scintillation in TeO$_2$ for beta and alpha particles.
- Validated optical model for TeO$_2$ light behavior.

## Abstract

Simultaneous measurement of phonon and light signatures is an effective way to reduce the backgrounds and increase the sensitivity of CUPID, a next-generation bolometric neutrinoless double-beta decay ($0\nu\beta\beta$) experiment. Light emission in tellurium dioxide (TeO$_2$) crystals, one of the candidate materials for CUPID, is dominated by faint Cherenkov radiation, and the high refractive index of TeO$_2$ complicates light collection. Positive identification of $0\nu\beta\beta$ events therefore requires high-sensitivity light detectors and careful optimization of light transport. A detailed microphysical understanding of the optical properties of TeO$_2$ crystals is essential for such optimization. We present a set of quantitative measurements of light production and transport in a cubic TeO$_2$ crystal, verified with a complete optical model and calibrated against a UVT acrylic standard. We measure the optical surface properties of the crystal, and set stringent limits on the amount of room-temperature scintillation in TeO$_2$ for $\beta$ and $\alpha$ particles of 5.3 and 8 photons / MeV, respectively, at 90% confidence. The techniques described here can be used to optimize and verify the particle identification capabilities of CUPID.