Collaborative Research Towards a tonne-scale bolometer-based neutrinoless double beta decay experiment (Final Report)
Cryogenic bolometers are an excellent technology for neutrinoless double beta decay searches owing to their very high energy resolution and potential for high radiopurity. The current most advanced large-scale experiment using these detectors is the Cryogenic Underground Observatory for Rare Events (CUORE). The largest source of background in CUORE is degraded alpha particles, emitted from shallow depths of the detector holders, which can deposit a thermal energy signature similar to neutrinoless double beta decay. To mitigate this background, the CUPID concept (CUORE Upgrade with Particle IDentification) proposes to use scintillating cryogenic detectors. Detecting both the scintillation light and the thermal signal allows discrimination between alpha particle events and beta/gamma events. We report on the design and execution of R&D tests to optimize the design of the single detector module, in particular the scintillation light collection efficiency at cryogenic temperatures.