Analysis of the Intermediate-State Contributions to Neutrinoless Double β − Decays

A comprehensive analysis of the structure of the nuclear matrix elements (NMEs) of neutrinoless double beta-minus ( 0 ν β - β - ) decays to the 0 + ground and first excited states is performed in terms of the contributing multipole states in the intermediate nuclei of 0 ν β - β - transitions. We concentrate on the transitions mediated by the light (l-NMEs) Majorana neutrinos. As nuclear model we use the proton-neutron quasiparticle random-phase approximation (pnQRPA) with a realistic two-nucleon interaction based on the Bonn one-boson-exchange G matrix. In the computations we include the appropriate short-range correlations, nucleon form factors, and higher-order nucleonic weak currents and restore the isospin symmetry by the isoscalar-isovector decomposition of the particle-particle proton-neutron interaction parameter g p p .