Model for the Cherenkov light emission of TeO$_{2}$ cryogenic calorimeters

TL;DR

This paper models Cherenkov light emission in TeO₂ cryogenic calorimeters, showing how surface roughness and detector design improvements can enhance alpha particle rejection, crucial for neutrino-less double beta decay experiments.

Contribution

It introduces a detailed Monte Carlo simulation of Cherenkov light in TeO₂ calorimeters and proposes methods to improve alpha background rejection.

Findings

Light yield can be increased by up to 60% with surface roughness enhancement.

Alpha rejection is feasible with high sensitivity light detectors.

Gamma rejection remains challenging.

Abstract

The most sensitive process able to probe the Majorana nature of neutrinos and discover Lepton Number Violation is the neutrino-less double beta decay. Thanks to the excellent energy resolution, efficiency and intrinsic radio-purity, cryogenic calorimeters are primed for the search for this process. A novel approach able to improve the sensitivity of the current experiments is the rejection of $\alpha$ interactions, that represents the dominant background source. In TeO$_2$ calorimeters, $\alpha$ particles can be tagged as, in contrast to electrons, they do not emit Cherenkov light. Nevertheless, the very low amount of detected Cherenkov light undermines the complete rejection of $\alpha$ background. In this paper we compare the results obtained in previous measurements of the TeO$_2$ light yield with a detailed Monte Carlo simulation able to reproduce the number of Cherenkov photons produced in $\beta/\gamma$ interactions within the calorimeter and their propagation in the experimental set-up. We demonstrate that the light yield detectable from a $5\times5\times5$~cm$^{3}$ TeO$_2$ bolometer can be increased by up to 60% by increasing the surface roughness of the crystal and improving the light detector design. Moreover, we study the possibility to disentangle $\alpha$, $\beta$ and $\gamma$ interactions, which represent the ultimate background source. Unfortunately $\gamma$ rejection is not feasible but $\alpha$ rejection can be achieved exploiting high sensitivity light detectors.