Development of \(^{100}\hbox {Mo}\)-containing scintillating bolometers for a high-sensitivity neutrinoless double-beta decay search

This paper reports on the development of a technology involving \(^{100}\hbox {Mo}\)-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass (\(\sim 1~\hbox {kg}\)), high optical quality, radiopure \(^{100}\hbox {Mo}\)-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2–0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the double-beta transition of \(^{100}\hbox {Mo}\) (3034 keV) is 4–6 keV FWHM. The rejection of the \(\alpha \)-induced dominant background above 2.6 MeV is better than \(8\sigma \). Less than \(10~\upmu \hbox {Bq/kg}\) activity of \(^{232}\hbox {Th}\, (^{228}\hbox {Th})\) and \(^{226}\hbox {Ra}\) in the crystals is ensured by boule recrystallization. The potential of \(^{100}\hbox {Mo}\)-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only \(10~\hbox {kg}\times \hbox {d}\) exposure: the two neutrino double-beta decay half-life of \(^{100}\hbox {Mo}\) has been measured with the up-to-date highest accuracy as \(T_{1/2}\) = [6.90 ± 0.15(stat.) ± 0.37(syst.)] \(\times ~10^{18}~\hbox {years}\). Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of \(^{100}\hbox {Mo}\).