Low-temperature light detectors for the CUPID experiment

CUPID is a proposed next-generation experiment that will search for neutrinoless double-β (0νββ) decay in ¹⁰⁰Mo using ~1600 Li₂¹⁰⁰MoO₄ scintillating crystals operated as low-temperature calorimeters close to ∼10mK. It will leverage the crystal’s energy loss mechanism to tag particle type by simultaneously measuring both the thermal and scintillation signals. We will use an auxiliary low-temperature calorimeter to detect light with high photon collection efficiency. The light detectors must have a very low energy threshold ??(100eV) and good timing resolution < 1 ms to tag α background and 2νββ pile-up events in the region of interest. The light detectors are crucial to reach the CUPID background goal of <10^-4 counts/(keV.kg.yr) for its baseline design. In this talk, I will briefly discuss the baseline design of the CUPID light detectors and the R&D status of a future upgrade with transition-edge sensor (TES) based light detectors which may further help suppress the pile-up background.