Search

The Heidelberg-Moscow experiment gives the most stringent limit on the Majorana neutrino mass. After 24 kg yr of data with pulse shape measurements, we set a lower limit on the half-life of the neutrinoless double beta decay in 76Ge of T_1/2 > 5.7 * 10^{25} yr at 90% C.L., thus excluding an effective Majorana neutrino mass greater than 0.2 eV. This allows to set strong constraints on degenerate neutrino mass models., 6 pages (latex) including 3 postscript figures and 2 tables

New constraints on the parameters of the minimal supersymmetric standard model with explicit $R$-parity violation ( ${R}_{p}$MSSM) are obtained from the current experimental lower bound on the half-life of ${}^{76}$Ge $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay. These constraints are shown to be more stringent than those from other low-energy processes and are competitive with or even more stringent than constraints expected from accelerator searches.

Motivated by a recent measurement of {beta}-delayed fission in the {sup 180}Tl{r arrow}{sup 180}Hg chain, we have calculated the {beta} strength distribution {ital S}{sub {beta}} of the neutron-deficient nuclide {sup 180}Tl within the framework of the proton-neutron quasiparticle random phase approximation ({ital pn}-QRPA). The fission barrier height is then deduced from the measured {beta}-delayed fission probability {ital P}{sub {beta}DF}. In addition, as a test for the reliability of the theoretical strength distributions, {beta}{sup +}/EC half-lives of some isotopic chains are calculated using the {ital pn}-QRPA including both particle-hole and particle-particle Gamow-Teller residual interactions.

We have examined the double-beta decay mode accompanied by Majoron emission. After 223 days of measurement corresponding to about 615 kg d or 19.3 mol yr of exposure we find a lower half-life limit for this decay channel of [ital T][sub 1/2][sup 0[nu][chi]][gt]1.66(1.99)[times]10[sup 22] yr [90% (68%) C.L.] yielding a new limit for the Majoron-neutrino coupling of [l angle][ital g][sub [nu][chi]][r angle][lt]1.8[times]10[sup [minus]4] (90% C.L.).