Effects of orbital occupancies on the neutrinoless ββ matrix element of 76Ge

In this work we use the recently measured neutron occupancies in the Ge-76 and Se-76 nuclei as a guideline to define the neutron quasiparticle states in the 1p0f0g shell. We define the proton quasiparticles by inspecting the odd-mass nuclei adjacent to Ge-76 and Se-76. We insert the resulting quasiparticles in a proton-neutron quasiparticle random-phase approximation (pnQRPA) calculation of the nuclear matrix element of the neutrinoless double beta (O nu beta beta) decay of Ge-76. A realistic model space and effective microscopic two-nucleon interactions are used. We include the nucleon-nucleon short-range correlations and other relevant corrections at the nucleon level. It is found that the resulting O nu beta beta matrix element is smaller than in the previous pnQRPA calculations, and closer to the recently reported shell-model results. (C) 2008 Published by Elsevier B.V.