Performance of a SiPM-based, plastic scintillator muon veto prototype for CUPID

CUPID will be a next-generation experiment searching for neutrinoless double beta decay in the inverted mass ordering regime. The reduction of backgrounds in the region of interest is critical to the performance of the experiment. Despite its underground location, muon-induced events will be a non-negligible source of background for CUPID, and their mitigation will be critical in reaching CUPID's target sensitivity. This mitigation will be achieved with a muon veto system, which must fit within the physical constraints of the existing infrastructure while maximizing geometrical coverage. We present the design, construction, and characterization of prototypes for a modular system of plastic scintillator panels with embedded plastic wavelength-shifting fibers connected to silicon photomultipliers for the CUPID muon veto. The 100 × 50 × 2.5 cm 3 panel prototype presented here exhibited a light yield of (55.9 ± 1.5) p.e./MeV with a position reconstruction resolution of 25 × 25 cm 2 . This design also achieves a muon detection efficiency of (98 ± 1)%. We compare the light yield, uniformity, and position reconstruction potential of different prototype designs.