Enhanced light signal for the suppression of pile-up events in Mo-based bolometers for the 0νββ decay search.

Random coincidences of events could be one of the main sources of background in the search for neutrinoless double-beta decay of Mo-100 with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li2MoO4 crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov-Trofimov-Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li2MoO4 scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index similar to 10(-4) counts/keV/kg/year with 280 g Li2MoO4 (Mo-100 enriched) bolometers at 3034 keV, the Q(beta beta) of the double-beta decay, and target the goal of a next generation experiment like CUPID.

Automated summary

This article presents an experimental work using NTL-LDs and Li2MoO4 scintillating bolometers in the CROSS experiment, and proposes a new analysis method based on a pulse-shape discrimination algorithm that provides high pile-up rejection efficiencies.