Neutrinoless double beta decay is a very rare nuclear transition, whose existence can provide essential information about neutrino properties like the hierarchy and the absolute mass scale. If observed, this process will prove that the lepton number conservation law can be violated and that we need to extend the Standard Model. The LUMINEU experiment (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature – French ANR project) is focused on the investigation of the molybdenum isotope 100Mo, which is an excellent candidate for double beta decay experiments (Q0νββ = 3034 keV , reasonably high natural isotopic abundance - 9.7 % and viable enrichment technology). The key-point of LUMINEU is the use of an innovative detection technology, based on cryogenic scintillating bolometers. A scintillating bolometer consists of an energy absorber (which embeds the bb isotope) equipped with a temperature sensor and coupled to a light detector. The signal, collected at very low temperatures (typically <20 mK for large bolometers), consists of a thermal pulse originated after an energy release in the crystal. If the absorber is also a scintillator we can collect in coincidence light signals, used to separate α and ϒ/β signals due to a different light output, when a particle is absorbed. The bolometric technique in used the so-called “source=detector” approach, joining high energy resolution and large efficiency.
LUMINEU is a successful R&D activity promoting the use of scintillating bolometers based on both ZnMoO4 and Li2MoO4 crystals for the investigation of 0νββ decay of 100Mo. In the framework of this experiment, many detectors have been tested underground at LSM and LNGS. In particular we have been able to produce different enriched scintillating crystals of Li2100MoO4 (100Mo enriched at 99.9% produced in NIIC (Novosibirsk, Russia)).
LUMINEU has paved the way for the next stage of the experiment, called CUPID-Mo, which will be a 20-crystal array of Li2100MoO4 ( ~ 3 kg of 100Mo) equipped with NTD Ge thermistors (special temperature sensors) and coupled to Ge light detectors. The main goal of CUPID-Mo is to prove the possibility to reach a background rate below 10-3 counts x kg x y. This demonstrator is part of the CUPID project, a proposed bolometric tonne-scale experiment thought as the follow-up of the CUORE experiment.
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