# Cryogenic light detectors with enhanced performance for rare events physics

## TL;DR

This paper introduces a simple gravity-based mounting method for bolometric light detectors that significantly improves light collection efficiency and energy resolution, advancing the performance of detectors for rare event physics like CUPID.

## Contribution

The paper presents a novel, straightforward mounting technique for bolometric light detectors that enhances efficiency and resolution, suitable for large-scale rare event experiments.

## Key findings

- Light collection efficiency increased by over 50%
- Achieved baseline energy resolution of 20 eV RMS
- Demonstrated excellent alpha/beta discrimination

## Abstract

We have developed and tested a new way of coupling bolometric light detectors to scintillating crystal bolometers based upon simply resting the light detector on the crystal surface, held in position only by gravity. This straightforward mounting results in three important improvements: (1) it decreases the amount of non-active materials needed to assemble the detector, (2) it substantially increases the light collection efficiency by minimizing the light losses induced by the mounting structure, and (3) it enhances the thermal signal induced in the light detector thanks to the extremely weak thermal link to the thermal bath. We tested this new technique with a 16 cm$^2$ Ge light detector with thermistor readout sitting on the surface of a large TeO$_2$ bolometer. The light collection efficiency was increased by greater than 50\% compared to previously tested alternative mountings. We obtained a baseline energy resolution on the light detector of 20~eV RMS that, together with increased light collection, enabled us to obtain the best $\alpha$ vs $\beta/\gamma$ discrimination ever obtained with massive TeO$_2$ crystals. At the same time we achieved rise and decay times of 0.8 and 1.6 ms, respectively. This superb performance meets all of the requirements for the CUPID (CUORE Upgrade with Particle IDentification) experiment, which is a 1-ton scintillating bolometer follow up to CUORE.