Double beta decay of ${}^{48}$Ca

Abstract

${}^{48}$Ca, the lightest double beta decay candidate, is the only one simple enough to be treated exactly in the nuclear shell model. Thus, the $\beta \beta (2\nu )$ half-life measurement, reported here, provides a unique test of the nuclear physics involved in the $\beta \beta$ matrix element calculation. Enriched ${}^{48}$Ca sources of two different thicknesses have been exposed in a time projection chamber, and yield T${}_{1/2}^{2\nu }=(4.3_{-1.1}^{+2.4}[stat.]\pm 1.4[syst.])\times 10^{19}$ years, compatible with the shell model calculations.

Comments: 4 pages, LaTex, 3 figures imbedded, PRL format