First Results from the AMoRE-Pilot neutrinoless double beta decay experiment

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