Search

Abstract The Advanced Mo-based Rare process Experiment (AMoRE)-Pilot experiment is an initial phase of the AMoRE search for neutrinoless double beta decay of $$^{100}$$ 100 Mo, with the purpose of investigating the level and sources of backgrounds. Searches for neutrinoless double beta decay generally require ultimately low backgrounds. Surface $$\alpha $$ α decays on the crystals themselves or nearby materials can deposit a continuum of energies that can be as high as the Q-value of the decay itself and may fall in the region of interest (ROI). To understand these background events, we studied backgrounds from radioactive contaminations internal to and on the surface of the crystals or nearby materials with Geant4-based Monte Carlo simulations. In this study, we report on the measured $$\alpha $$ α energy spectra fitted with the corresponding simulated spectra for six crystal detectors, where sources of background contributions could be identified through high energy $$\alpha $$ α peaks and continuum parts in the energy spectrum for both internal and surface contaminations. We determine the low-energy contributions from internal and surface $$\alpha $$ α contaminations by extrapolating from the $$\alpha $$ α background fitting model.

Abstract The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay ($$0\nu \beta \beta $$ 0νββ ) of $$^{100}$$ 100 Mo with $$\sim 100\,\hbox {kg}$$ ∼100kg of $$^{100}$$ 100 Mo-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 $$^{48}$$ 48 Ca-depleted calcium and $$^{100}$$ 100 Mo-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 $$^{100}$$ 100 Mo is found, and a upper limit is set for the half-life of $$0\nu \beta \beta $$ 0νββ of $$^{100}$$ 100 Mo 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 .