Development of MMC-based lithium molybdate cryogenic calorimeters for AMoRE-II

TL;DR

This paper reports on the design and testing of lithium molybdate cryogenic calorimeters for the upcoming AMoRE-II experiment, demonstrating promising energy resolution, particle discrimination, and operational stability at higher temperatures.

Contribution

It introduces the baseline design and characterization of lithium molybdate calorimeters for AMoRE-II, including prototype results with improved housing and larger crystals at 10 mK.

Findings

Energy resolution of 7.55 - 8.82 keV at 2.615 MeV

Effective light detection of 0.79 - 0.96 keV/MeV

Alpha particle discrimination power of 12.37 - 19.50

Abstract

The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517 - 521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55 - 8.82 keV at the 2.615 MeV $^{208}$Tl $\gamma$ line, and effective light detection of 0.79 - 0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37 - 19.50 at the energy region around $^6$Li(n, $\alpha$)$^3$H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array.