Two-neutrino double beta decay of 76Ge within deformed QRPA

Abstract

The effect of deformation on the two-neutrino double decay (2νββ-decay) for ground state transition 76 Ge → 76 Se is studied in the framework of the deformed QRPA with separable Gamow-Teller residual interaction. A new suppression mechanism of the 2νββ-decay matrix element based on the difference in deformations of the initial and final nuclei is included. An advantage of this suppression mechanism in comparison with that associated with ground state correlations is that it allows a simultaneous description of the single β and the 2νββ-decay. By performing a detail calculation of the 2νββ-decay of 76 Ge, it is found that the states of intermediate nucleus lying in the region of the Gamow-Teller resonance contribute significantly to the matrix element of this process.

Nuclear matrix elements for neutrinoless double-beta decay and double-electron capture

“…A QRPA approach for calculating ββ-decay amplitudes in deformed nuclei has been developed in a series of papers [32][33][34][35][36]. M 2ν were calculated in Refs.…”

“…(31) corresponds to the overlap factor of the initial and final BCS vacua in the form given in Ref. [32]. The matrix element M 0ν is given within the QRPA in the intrinsic system by a sum of the partial amplitudes of transitions via all the intermediate states K π :…”

Overlap of quasiparticle random-phase approximation states for nuclear matrix elements of the neutrino-less double-βdecay

“…The advantage of this approach is that the intermediate states are free from the problem of how to treat the odd particle without any modification because they are states of even-even nuclei. In addition, we calculate the overlap of the intermediate states obtained by the like-particle QRPA with greater accuracy than that in the previous studies [7,14,[21][22][23]. It is emphasized that the importance of the overlap of the intermediate states has been pointed out in Ref.…”

“…It is emphasized that the importance of the overlap of the intermediate states has been pointed out in Ref. [14] in terms of deformation. The purpose of this study is to demonstrate the feasibility of the overlap calculation using the ground-state wave function of the like-particle QRPA explicitly.…”

“…A few of the milestones include the correct treatment of the effects of the Pauli-exclusion principle in the intermediate states by the renormalized pn-QRPA [11], fulfillment of the Ikeda sum rule by the fully renormalized pn-QRPA [12], inclusion of the pnpairing correlations [13], and extension to the deformed states [14]. Nevertheless, the nuclear matrix elements calculated by various approaches including the pn-QRPA are distributed in a range of a factor of 2 [3,15].…”