Calculation of the beta and beta beta decay observables of 48Ca using QRPA with and without particle-number projection

Abstract

The double beta decay ( beta beta ) of 48Ca to the ground state of 48Ti is analysed using the quasiparticle random phase approximation with (PQRPA) and without (QRPA) particle-number projection. The pairing interaction strength and the strength of other multipole channels of the renormalized G matrix interaction are adjusted to yield optimal beta - and beta + decay properties of 48Ca and 48Ti and to comply with the experimental limits of the 2 nu beta beta decay half-life. Nuclear matrix elements of the 0 nu beta beta decay transition are then calculated using the QRPA and PQRPA parameter-free to yield an estimate of the Majorana neutrino mass. In addition, the contribution of the right-handed weak currents is studied. The number projection is found to be important for light nuclei near magic numbers. The gA/gV ratio of the weak axial vector and vector coupling coefficients is found to be renormalized by the dynamics of the effective weak transition operators derived from a relativistic quark-confinement model.