Multilayer Scintillator Responses for Mo Observatory of Neutrino Experiment Studied Using a Prototype Detector MOON-1

An ensemble of multilayer scintillators is discussed as an option of the high-sensitivity detector MOON (Mo Observatory of Neutrinos) for spectroscopic measurements of neutrinoless double beta decays. A prototype detector MOON-1, which consists of 6-layer plastic scintillator plates, was built to study the photon responses of the MOON-type detector. The photon responses, i.e., the number of scintillation photons collected and the energy resolution, which are key elements for high-sensitivity experiments, are found to be 1835±30 photoelectrons for 976 keV electrons and σ=2.9±0.1% (Δ E / E =6.8±0.3% in FWHM) at the Q ββ ∼3 MeV region, respectively. The multilayer plastic scintillator structure with high energy resolution as well as a good signal for the background suppression of β–γ rays is crucial for the MOON-type detector to achieve inverted-hierarchy neutrino-mass sensitivity. It will also be useful for medical and other rare-decay experiments as well.