Optimization of cryogenic calorimetric detection with lithium molybdate crystals for AMoRE-II experiments

The AMoRE collaboration is preparing for the second phase of the experiment, AMoRE-II, which will exploit a 100 kg of ¹⁰⁰Mo isotopes to search for neutrinoless double beta decay from the isotope. Most of the ¹⁰⁰Mo isotopes will be contained in the lithium molybdate (Li₂MoO₄) crystals, which will act as absorbers of cryogenic calorimeters coupled to MMC (metallic magnetic calorimeter) sensors. The detector array will have a total mass of approximately 200 kg with hundreds of detector modules. Hence, considerable effort has been taken to optimize the lithium molybdate crystal detector in terms of the detector performance and preparation procedure to build many detector modules in a reasonable schedule without compromising the detector performance. We found some critical experimental conditions to improve the energy resolution in a series of test experiments. In this paper, we discuss the effect of surface treatment and thermal link connection in improving the energy resolution from 14-15 keV to below 7 keV at 2.615 MeV, ²⁰⁸Tl gamma line, which is near the Q-value of the decay of ¹⁰⁰Mo, 3.034MeV. We also report the high discrimination power for the separation of alpha particles using the simultaneous scintillation light detection with a test performed in the cryogen-free dilution refrigerator.