CANDLES - Search for Neutrino-less Double Beta Decay of $^{48}$Ca -.
摘要
Abstract. CANDLES is the project to search for neutrino-less double beta decay (0νββ) of 48Ca. The observation of 0νββ will prove existence of a massive Majorana neutrino. For the 0νββ measurement, we need a low background condition because of a low decay rate of 0νββ. Now we installed the CANDLES III system at the Kamioka underground laboratory. The CANDLES III system realizes the low background condition by a char-acteristic structure and data analyses for background rejection. Here we report perfor-mances of the CANDLES III system. 1 Double beta decay of 48Ca The neutrino-less double beta decay is acquiring great interest after the confirmation of neutrino os-cillation which demonstrated nonzero neutrino mass. Measurement of 0νββ provides a test for the Majorana nature of neutrinos and gives an absolute scale of the effective neutrino mass. Many exper-iments have been carried out so far and many projects have been proposed. Among double beta decay nuclei, 48Ca has an advantage of the highest Qββ-value (4.27 MeV). This large Qββ-value gives a large phase-space factor to enhance the 0νββ rate and the least contribution from natural background radiations in the energy region of the Qββ-value. Therefore good signal to