Assessment of uncertainties in QRPA 0νββ-decay nuclear matrix elements

The nuclear matrix elements M-0v of the neutrinoless double beta decay (0v beta beta) of most nuclei with known 2v beta beta-decay rates are systematically evaluated using the quasiparticle random phase approximation (QRPA) and renormalized QRPA (RQRPA). The experimental 2v beta beta-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. New results confirm that with such procedure the M-0v values become essentially independent on the size of the single-particle basis. Furthermore, the matrix elements are shown to be also rather stable with respect to the possible quenching of the axial vector strength parametrized by reducing the coupling constant g(A), as well as to the uncertainties of parameters describing the short range nucleon correlations. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. Furthermore, a discussion of other implicit and explicit parameters, inherent to the QRPA method, is presented. Comparison is made of the ways these factors are chosen by different authors. It is suggested that most of the spread among the published 0v beta beta decay nuclear matrix elements can be ascribed to these choices. (c) 2005 Elsevier B.V. All rights reserved.