Nuclear matrix elements for the 0νββ(0+ → 2+) decay of 76Ge within the two-nucleon mechanism

In this paper, we present the first beyond closure calculation for the neutrinoless double-beta decay of Ge-76 to the first 2(+) states of Se-76 within the two nucleon mechanism. The isospin symmetry restored quasiparticle random-phase approximation method with the charge-dependent-Bonn realistic force is adopted for the nuclear structure calculations. We analyze the structure of the nuclear matrix elements and estimate the uncertainties from our nuclear many-body calculations. We find g(pp) plays an important role for the calculations, and if quenching is included, suppression for the transition matrix element M-lambda is found. Our results for the transition matrix elements are about one order of magnitude larger than previous projected Hartree-Fock-Bogolyubov results with the closure approximation.