Suppression of the two-neutrino double-beta decay by nuclear-structure effects

Abstract

The nuclear matrix element for 2v double-beta decay is calculated within the quasiparticle randomphase approximation. It is shown that the decay matrix element passes through zero as a function of the strength g^^ of the particle-particle component of the spin-isospin polarization force, neglected previously. The analysis of electron capture/^"*" decay rates for semimagic neutron-deficient nuclei suggests values for g^^ in the very vicinity of this zero, which gives rise to long lifetimes. The qualitative features of nuclear fiP decay are illustrated with the example of an exactly soluble model.

Neutrinoless ββ nuclear matrix elements using isovector spin-dipole Jπ=2− data

“…Traditionally the g ph parameter is fixed by fitting the centroid of the Gamow-Teller resonance (GTR) in the 1 + channel of the calculations [1,38,39,48,49]. This same g ph is then used for all multipoles J π .…”

IGEX76Geneutrinoless double-beta decay experiment: Prospects for next generation experiments

“…This quantity derives from nuclear structure calculations and is model dependent as seen in Table 1 In 1986, the CalTech group [25] introduced the Quasiparticle Random Phase Approximation (QRPA) with three parameters to account for pairing, particle-hole, and particle-particle interactions. Later, similar models were developed by the Tübingen group [26] and the Hiedelberg group [27].…”

Description of double β decay within the continuum quasiparticle random-phase approximation

“…(the same approximation as used in Refs. [23,24]), the amplitude (21) is simply given by one-half of the corresponding static nuclear polarizability with respect to the external s.p. field ßτ − :…”