Article:

Abstract

The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay (0νββ) of ¹⁰⁰Mo with ∼ 100 kg of ¹⁰⁰Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from ⁴⁸Ca-depleted calcium and ¹⁰⁰ Mo-enriched molybdenum (^48deplCa¹⁰⁰MoO₄). The simultaneous detection of heat (phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot 0νββ search with a 111 kg day live exposure of ^48deplCa¹⁰⁰MoO₄ crystals. No evidence for 0νββ decay of ¹⁰⁰Mo is found, and a upper limit is set for the half-life of 0νββ of ¹⁰⁰Mo of T^0ν > 9.5 × 1022 years at 90% C.L. This limit corresponds 1/2 to an effective Majorana neutrino mass limit in the range ⟩ ≤ (1.2 − 2.1)eV.

Conclusion

In summary, we find no evidence of 0νββ decay of 100Mo with a live exposure of 111 kg day using ^48deplCa¹⁰⁰MoO₄ crystals. An upper limit of T^0ν>9.5×1022 years is achieved 1/2 results in reduced background levels from unresolved pileup signals in rare event searches.

After the completion of the Pilot runs, AMoRE-I will be implemented with 18 crystals. These include seven additional ^48deplCa¹⁰⁰MoO₄ that are already on hand. In addition, five ¹⁰⁰Mo-enriched Li₂MoO₄ and Na₂MoO₄ crystals that are currently being fabricated. The total mass of the AMoRE-I crystals will be approximately 6 kg (3 kg of ¹⁰⁰Mo). The internal backgrounds and detector performance in phonon- scintillation detection will be investigated to determine the type of crystals to be used for the AMoRE-II, the main phase of the project with a total crystal mass of 200 kg. AMoRE- II aims at improving the effective Majorana neutrino mass sensitivity to 20–50 meV. It will be installed in Yemi lab, a new 1000 m deep underground laboratory that is under construction in Korea and will be available in 2020.

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