Enhanced light signal for the suppression of pile-up events in Mo-based bolometers for the 0$$\nu \beta \beta $$ decay search.

Abstract

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of $$^{100}$$ 100 Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li$$_2$$ 2 MoO$$_4$$ 4 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 Li$$_2$$ 2 MoO$$_4$$ 4 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 $$\sim $$ ∼ $$10^{-4}$$ 10 - 4 counts/keV/kg/year with 280 g Li$$_2$$ 2 MoO$$_4$$ 4 ($$^{100}$$ 100 Mo enriched) bolometers at 3034 keV, the Q$$_{\beta \beta }$$ β β of the double-beta decay, and target the goal of a next generation experiment like CUPID.

Test of 116CdWO4 and Li2MoO4 scintillating bolometers in the CROSS underground facility with upgraded detector suspension

“…In the case of the light detector (LD-LMO) coupled to the Li 2 MoO 4 bolometer, we enhanced its performance by applying a 60 V bias on the Al electrode; it allowed us to get a high sensitivity of about 10-30 μV/keV and a baseline noise of only 16-18 eV FWHM (depending on the working point). These results additionally demonstrate how powerful and viable is the Neganov-Trofimov-Luke signal amplification for the improvement of the signal-to-noise ratio of light detectors, which is of special interest for pile-up background rejection [57,68].…”

“…The selection efficiency (including the trigger efficiency) has been investigated using a pulse-injection method as described e.g. in [57]; we found the efficiency of 97% in the region of interest for 𝛼 particles. The energy spectrum of the selected 𝛼 events is shown in figure 7.…”

“…The used source is made of a thoriated tungsten wire which was inserted inside the lead shield for calibration runs. A part of the data collected was dedicated to studies of pile-up rejection efficiency for next-generation 100 Mo-based bolometric 0𝜈2𝛽 experiments; an interested reader can find details and results of this investigation in [57]. Unfortunately, after about one month of the operation, the cryogenic run was terminated by the failure of the primary circulation pump.…”

“…Here (section 4) we present results for the 2 kS/s sampling and 300 Hz Bessel cut-off; data acquired with the higher sampling (and the Bessel cut-off frequency) are devoted to pile-up rejection study reported in [57].…”

Twelve-crystal prototype of Li2MoO4 scintillating bolometers for CUPID and CROSS experiments

“…Fast time response is essential for LMO scintillating bolometers as a viable tool for the rejection of pile-up events, i.e. a source of a notable background in 100 Mo-enriched thermal detectors for 0𝜈𝛽𝛽 decay search [89][90][91][92][93]. In order to characterize a time response of each triggered signal, we computed the following two parameters: 1) rise time defined as the time required by the signal to increase from 10% to 90% of its height; 2) decay time, the time required to decrease from 90% to 30% of its height.…”