GT neutrino–nuclear responses for double beta decays and astro neutrinos

Abstract

Gamow–Teller nuclear matrix elements (NMEs) for pairs of ground-state-to-ground-state transitions, in particular their geometric mean NME , are studied. The observed means in the medium-heavy mass region are compared with the corresponding single-quasiparticle (qp) NMEs and the means calculated by the proton neutron qp random-phase approximation (pnQRPA). The NMEs turn out to be insensitive to the nucleon occupancy/vacancy amplitudes and to the particle–particle interaction parameter of the pnQRPA. The observed mean NMEs are found to be reduced by a coefficient relative to the effective qp NMEs and by a coefficient with respect to the pnQRPA NMEs. The reductions associated with the spin isospin correlations and nuclear medium effects, and their impact on nuclear double beta decays and astro-neutrino–nuclear interactions are discussed.