A search for the double beta decay of 48Ca and lepton conservation

Abstract

Although recent mass-spectrometer experiments have shown convincingly that double beta decay does take place, observation of the decay electron spectrum is necessary to be certain whether two neutrinos are emitted (as expected assuming lepton conservation) or none (implying lepton nonconservation). An attempt to measure the electron spectrum from the double beta decay of 48 Ca was made in a deep salt mine, using a streamer chamber in a magnetic field. In 1150 hours of observation with a 10.6 g source, only one event was seen which might be neutrinoless double beta decay, implying a half-life of > 2 × 10 21 y at the 80% confidence level. This in turn implies that any violation of lepton conservation must be of the order of 10 −3 or less. A half-life limit of > 3.6 × 10 19 y for the two-neutrino mode of 48 Ca double beta decay was also obtained.