Secular Equilibrium Assessment in a $\mathrm{CaWO}_4$ Target Crystal from the Dark Matter Experiment CRESST using Bayesian Likelihood Normalisation

TL;DR

This study evaluates the validity of secular equilibrium assumptions in the CRESST dark matter experiment's calcium tungstate detector using Bayesian likelihood methods, revealing deviations that warrant further investigation.

Contribution

It introduces a Bayesian likelihood-based spectral template normalization approach to test secular equilibrium in the detector, highlighting potential deviations from equilibrium assumptions.

Findings

Deviations from secular equilibrium were observed.

Bayesian likelihood normalization was successfully applied.

Further investigations are needed to understand the deviations.

Abstract

CRESST is a leading direct detection sub-$\mathrm{GeVc}^{-2}$ dark matter experiment. During its second phase, cryogenic bolometers were used to detect nuclear recoils off the $\mathrm{CaWO}_4$ target crystal nuclei. The previously established electromagnetic background model relies on secular equilibrium (SE) assumptions. In this work, a validation of SE is attempted by comparing two likelihood-based normalisation results using a recently developed spectral template normalisation method based on Bayesian likelihood. We find deviations from SE; further investigations are necessary to determine their origin.