Search for neutrino-less double beta decay of 48Ca by CaF2 scintillator Original Research Article

A CaF2 scintillation detector system (ELEGANT VI) has been operating at Oto Cosmo Observatory to study double beta decays of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life of the neutrino-less double beta decay of 48Ca, the expected number of background events in that energy region was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF2 crystals. A new lower limit is obtained to be 1.4×1022 yr at the 90% C.L. An experimental sensitivity is 5.9×1021 yr at the 90% C.L.