Test Measurements of an MMC-Based 516-g Lithium Molybdate Crystal Detector for the AMoRE-II Experiment

The AMoRE collaboration is preparing for the AMoRE-II experiment that will probe neutrinoless double beta decay with 100 kg of 100 Mo isotope. The 100 Mo nuclide will be mainly in the form of lithium molybdate crystals that are instrumented with metallic magnetic calorimeters (MMC), which detect the phonon excitations produced by electrons from neutrinoless double beta decay in the crystals. The energy resolution at a Q -value = 3.034 MeV is around 10 keV within a temperature ranging between 10 and 20 mK. Increasing the crystal mass of individual detector modules will reduce the number of detector channels and allow a few practical advantages associated with crystal growing, detector preparation, and operation of the experiment. To this end, we carried out an experiment with a 6 cm (diameter (D)) × 6 cm (height (H)) cylindrical lithium molybdate crystal of 516 g mass, which is 73% more massive than the 5 cm (D) × 5 cm (H) crystals that are currently being used in the AMoRE-I setup. We found that the larger crystal detector shows good performance characteristics in terms of energy resolution, signal time constant and particle identification capability, which makes it a suitable option for the AMoRE-II experiment.