Calculation of double-beta-decay rates and the neutrino mass

Abstract

Predictions for 2ν and 0ν double-beta-decay rates are given for all nuclei withA≥70, for which double beta decay is energetically allowed. These predictions are based on detailed nuclear structure studies of the beta strength distribution and replace earlier estimates basing mostly on phase space considerations. New and more stringent limits on the Majorana neutrino mass are deduced from existing double-betadecay experiments. If is found that a proper treatment of the collective effects arising from spin-isospin as well as quadrupole-quadrupole forces leads to a strong reduction of the nuclear matrix elements for two-neutrino double beta decay, but has only minor influence on the matrix elementsM0ν for the neutrinoless decay mode. The smaller limits formν result, therefore, mainly from the fact that the widely used scaling procedure underestimates the 0ν matrix elements. It is further discussed to what extent interference between different neutrinos affects the obtained mass limits.