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Among the direct searches for WIMP-type dark matter, the DAMA experiment is unique in that it has consistently reported a positive signal for an annual-modulation signal with a large (9.3σ) statistical significance. This result is controversial because if it is interpreted as a signature for WIMP interactions, it conflicts with other direct search experiments that report null signals in the regions of parameter space that are allowed by the DAMA observation. This necessitates an independent verification of the origin of the observed modulation signal using the same technique as that employed by the DAMA experiment, namely low-background NaI(Tl) crystal detectors. Here, we report first results of a program of NaI(Tl) crystal measurements at the Yangyang Underground Laboratory aimed at producing NaI(Tl) crystal detectors with lower background levels and higher light yields than those used for the DAMA measurements.

The Korea Invisible Mass Search (KIMS) collaboration has developed low-background NaI(Tl) crystals that are suitable for the direct detection of WIMP dark matter. Building on experience accumulated during the KIMS-CsI programs, the KIMS-NaI experiment will consist of a 200 kg NaI(Tl) crystal array surrounded by layers of shielding structures and will be operated at the Yangyang underground laboratory. The goal is to provide an unambiguous test of the DAMA/LIBRA annual modulation signature. Measurements of six prototype crystals show progress in the reduction of internal contamination from radioisotopes. Based on our understanding of these measurements, we expect to achieve a background level in the final detector configuration that is less than 1 count/day/keV/kg for recoil energies around 2 keV. The annual modulation sensitivity for the KIMS-NaI experiment shows that an unambiguous 7σ test of the DAMA/LIBRA signature would be possible with a 600 kg year exposure with this system.

The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay ($$0\nu \beta \beta $$0νββ) of $$^{100}$$100Mo with $$\sim 100\,\hbox {kg}$$∼100kg of $$^{100}$$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 $$^{48}$$48Ca-depleted calcium and $$^{100}$$100Mo-enriched molybdenum ($$^{48{{\text {depl}}}}\hbox {Ca}^{100}\hbox {MoO}_{4}$$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 $$0\nu \beta \beta $$0νββ search with a 111 kg day live exposure of $$^{48{{\text {depl}}}}\hbox {Ca}^{100}\hbox {MoO}_{4}$$48deplCa100MoO4 crystals. No evidence for $$0\nu \beta \beta $$0νββ decay of $$^{100}$$100Mo is found, and a upper limit is set for the half-life of $$0\nu \beta \beta $$0νββ of $$^{100}$$100Mo of $$T^{0\nu }_{1/2} > 9.5\times 10^{22}~\hbox {years}$$T1/20ν>9.5×1022years at 90% C.L. This limit corresponds to an effective Majorana neutrino mass limit in the range $$\langle m_{\beta \beta }\rangle \le (1.2-2.1)\,\hbox {eV}$$⟨mββ⟩≤(1.2-2.1)eV.

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