Neutrinoless double-β-decay matrix elements within the second quasirandom phase approximation method

A computation of the neutrinoless double-β-decay matrix elements is performed with the second quasirandom phase approximation method [A. A. Raduta, A. Faessler, S. Stoica, and W. A. Kaminski, Phys. Lett. B 254, 7 (1991); A. A. Raduta, A. Faessler, and S. Stoica, Nucl. Phys. A534, 149 (1991); S. Stoica and W. A. Kaminski, Phys. Rev. C 47, 867 (1993); S. Stoica, ibid. 49, 787 (1994); Phys. Lett. B 350, 152 (1995); S. Stoica and I. Mihut, Nucl. Phys. A602, 197 (1996)] for the nuclei with $A=76,$ 82, 96, 100, 116, 128, 130, and 136. It was found that the Ikeda sum rule is fulfilled with good accuracy and the results display a weak dependence on the single particle basis used. Comparing our calculations with similar ones performed with other quasirandom phase approximation–based methods we estimate more precisely the accuracy of these methods in the prediction of the neutrinoless matrix elements and neutrino mass parameter, which is settled to about 50% from their calculated values. Taking the most recent experimental limits for the neutrinoless half-lives, we also deduced new limits for the neutrino mass parameter.