Suppression of 2νββ pile-up events in CUPID using light detectors.

CUPID (CUORE Upgrade with Particle ID) is a proposed tonne-scale 0νββ experiment that will use arrays of low-temperature calorimeters to probe the Majorana nature of neutrinos. CUPID will do background rejection by reading phonon and photon signals simultaneously from a scintillating Lithium Molybdate (Li₂¹⁰⁰MoO₄) crystal. The pile-up of ¹⁰⁰Mo ordinary 2νββ decay events in a single crystal will contribute to a non-negligible background in the region of interest. It cannot be rejected based on timing information from the massive LMO crystals since their response is slow. CUPID plans to use faster light detectors to reject the pile-up events based on pulse shape analysis. In this talk, I will review the two key technologies, (i) Neganov-Luke amplified phonon detectors with NTD-Ge sensors which provide excellent SNR, and (ii) Superconducting transition-edge sensors which have excellent timing resolution, that the CUPID collaboration has pursued. I will also briefly discuss how it may be necessary to combine both technologies to achieve the background goal for CUPID-1T, a next-next-generation experiment.