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.

The AMoRE (Advanced Mo-based Rare process Experiment) project is a series of experiments that use advanced cryogenic techniques to search for the neutrinoless double-beta decay of 100 Mo. The work is being carried out by an international collaboration of researchers from eight countries. These searches involve high precision measurements of radiation-induced temperature changes and scintillation light produced in ultra-pure 100 Mo-enriched and 48 Ca-depleted calcium molybdate ( 48depl Ca 100 MoO 4 ) crystals that are located in a deep underground laboratory in Korea. The 100 Mo nuclide was chosen for this 0νββ decay search because of its high Q-value and favorable nuclear matrix element. Tests have demonstrated that CaMoO 4 crystals produce the brightest scintillation light among all of the molybdate crystals, both at room and at cryogenic temperatures. 48depl Ca 100 MoO 4 crystals are being operated at milli-Kelvin temperatures and read out via specially developed metallic-magnetic-calorimeter (MMC) temperature sensors that have excellent energy resolution and relatively fast response times. The excellent energy resolution provides good discrimination of signal from backgrounds, and the fast response time is important for minimizing the irreducible background caused by random coincidence of two-neutrino double-beta decay events of 100 Mo nuclei. Comparisons of the scintillating-light and phonon yields and pulse shape discrimination of the phonon signals will be used to provide redundant rejection of alpha-ray-induced backgrounds. An effective Majorana neutrino mass sensitivity that reaches the expected range of the inverted neutrino mass hierarchy, i.e., 20-50 meV, could be achieved with a 200 kg array of 48depl Ca 100 MoO 4 crystals operating for three years.

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grown by a Czochralski method. Syntheses of the polycrystalline materials are discussed based on the thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis and the crystals' structures are reported based on the X-ray powder diffraction (XRD) analysis. Luminescence properties of the crystals from room temperature to 10 K are studied by exciting the crystal with a 280 nm light emitting diode (LED). The scintillation light yields of the crystals at different low temperatures are studied by exciting the crystal with strontium-90 ( 90 Sr) beta source. The developed crystals are not luminescent at room temperature. At cryogenic temperature, however, they become luminescent with longer decay times. This work also reports on the luminescence and scintillation properties of ZnMoO 4 , PbMoO 4 , Pb 2 MoO 5 , and CaMoO 4 crystals which have been grown at other institutes. The newly developed crystals' results are compared with the result of a standard CaMoO 4 crystal. Among the new Mo-based crystals, the Na 2 Mo 2 O 7 crystal shows the most promising properties for the neutrino-less double beta decay (0 ) search experiments at cryogenic temperature.

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