Ab initio neutrinoless double-beta decay matrix elements for 48Ca, 76Ge, and 82Se

TL;DR

This paper presents ab initio calculations of neutrinoless double-beta decay nuclear matrix elements for 48Ca, 76Ge, and 82Se, advancing first-principles understanding of these processes crucial for neutrino physics.

Contribution

The study introduces a consistent ab initio approach using in-medium similarity renormalization group to compute decay matrix elements, including tensor components, for key candidate nuclei.

Findings

Nuclear matrix elements are 25-45% smaller than phenomenological shell model results.

Tensor components are significant in 76Ge and 82Se.

Work paves the way for first-principles calculations in neutrinoless double-beta decay.

Abstract

We calculate basis-space converged neutrinoless $\beta \beta$ decay nuclear matrix elements for the lightest candidates: 48Ca, 76Ge and 82Se. Starting from initial two- and three-nucleon forces, we apply the ab initio in-medium similarity renormalization group to construct valence-space Hamiltonians and consistently transformed $\beta \beta$-decay operators. We find that the tensor component is non-negligible in 76Ge and 82Se, and resulting nuclear matrix elements are overall 25-45% smaller than those obtained from the phenomenological shell model. While a final matrix element with uncertainties still requires substantial developments, this work nevertheless opens a path toward a true first-principles calculation of neutrinoless $\beta \beta$ decay in all nuclei relevant for ongoing large-scale searches.