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

Abstract: CUPID will be a next-generation experiment to search 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 backgrounds for CUPID, and mitigating them is critical to achieving CUPID's target sensitivity. Module prototypes were designed, built, and characterized for a muon veto. CUPID's muon veto system must fit within the physical constraints of the existing infrastructure while maximizing geometrical coverage. A modular system of plastic scintillator panels with embedded plastic wavelength-shifting fibers connected to silicon photomultiplier light detectors is proposed for the CUPID muon tagger. The 100$\times$50 cm$^2$ panel prototype presented here exhibited a light yield of ($57.2 \pm 4.0$) p.e. per MeV, with a position reconstruction resolution of 25$\times$ 25 cm$^2$. This design also achieves a detection efficiency of $(98\pm1)\%$. This paper describes the development, characterization, and testing of prototype modules for the CUPID muon veto. We compare the light yield, uniformity, and position reconstruction potential of different prototype designs.