Double beta decay of48Ca

Abstract

48Ca, the lightest double beta decay candidate, has been until now the only one simple enough to be treated exactly in the nuclear shell model. Thus, theββ(2ν) half-life measurement, reported here, provides a unique test of the nuclear physics involved in theββ matrix element calculation. Enriched48Ca sources of two different thicknesses have been exposed in a time projection chamber, and yieldT12/2ν=(4.3−1.1+2.4[stat.] ± 1.4[syst.]) × 1019 years, compatible with the shell model calculations. The consequences of this result for the shell model calculation of theββ(2ν) rate are briefly discussed.