Rejection of randomly coinciding events in Li$_2^{100}\mathrm{MoO}_4$ scintillating bolometers using light detectors based on the Neganov–Luke effect
Résumé
Random coincidences of nuclear events can be one of the main background sources in low-temperature calorimetric experiments looking for neutrinoless double-beta decay, especially in those searches based on scintillating bolometers embedding the promising double-beta candidate$^{100}$ Mo, because of the relatively short half-life of the two-neutrino double-beta decay of this nucleus. We show in this work that randomly coinciding events of the two-neutrino double-beta decay of$^{100}$ Mo in enriched Li$_2^{100}\,\mathrm{MoO}_4$ detectors can be effectively discriminated by pulse-shape analysis in the light channel if the scintillating bolometer is provided with a Neganov–Luke light detector, which can improve the signal-to-noise ratio by a large factor, assumed here at the level of ${\sim }750$ on the basis of preliminary experimental results obtained with these devices. The achieved pile-up rejection efficiency results in a very low contribution, of the order of ${\sim }6\times 10^{-5}$ counts/(keV $\cdot $ kg $\cdot $ y), to the background counting rate in the region of interest for a large volume ( ${\sim }90$ cm$^3$ ) Li$_2^{100}\,\mathrm{MoO}_4$ detector. This background level is very encouraging in view of a possible use of the Li$_2^{100}\,\mathrm{MoO}_4$ solution for a bolometric tonne-scale next-generation experiment as that proposed in the CUPID project.