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

In this work we use the recently measured neutron occupancies in the 76Ge and 76Se 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 76Ge and 76Se. 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 (0νββ0νββ) decay of 76Ge. 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 0νββ0νββ matrix element is smaller than in the previous pnQRPA calculations, and closer to the recently reported shell-model results.