Impact of the leading-order short-range nuclear matrix element on the neutrinoless double-beta decay of medium-mass and heavy nuclei

Abstract

We evaluate the leading-order short-range nuclear matrix element for the neutrinoless double-beta () decay of the nuclei most relevant for experiments, including 76Ge, 100Mo, 130Te and 136Xe. In our calculations, performed with the nuclear shell model and proton-neutron quasiparticle random-phase approximation (pnQRPA) methods, we estimate the coupling of this term by the contact charge-independence-breaking coupling of various nuclear Hamiltonians. Our results suggest a significant impact of the short-range matrix element, which is about and of the standard -decay long-range matrix element for the shell model and pnQRPA, respectively. Combining the full matrix elements with the results from current -decay experiments we find that, if both matrix elements carry the same sign, these searches move notably toward probing the inverted mass ordering of neutrino masses.