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

Abstract A CaF 2 scintillation detector system (ELEGANT VI) has been operating at Oto Cosmo Observatory to study double beta decays of 48 Ca. 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 48 Ca, the expected number of background events in that energy region was estimated by a Monte Carlo simulation using the measured activities of 214 Bi and 220 Rn inside CaF 2 crystals. A new lower limit is obtained to be 1.4×10 22  yr at the 90% C.L. An experimental sensitivity is 5.9×10 21  yr at the 90% C.L.