Continuum and Three-Nucleon Force Effects on 9Be Energy Levels

TL;DR

This paper extends the ab initio no-core shell model with continuum to include three-nucleon forces, improving the accuracy of energy level predictions in 9Be and highlighting the importance of continuum effects and 3N interactions.

Contribution

It introduces an extended approach to include 3N forces and continuum effects in ab initio calculations of p- and lower-sd-shell nuclei, applied to 9Be.

Findings

Continuum inclusion improves agreement with experimental energy levels.

Proper treatment of continuum is essential for assessing 3N interactions.

The 1/2+ resonance energy matches experimental data well.

Abstract

We extend the recently proposed ab initio no-core shell model with continuum to include three-nucleon (3N) interactions beyond the few-body domain. The extended approach allows for the assessment of effects of continuum degrees of freedom as well as of the 3N force in ab initio calculations of structure and reaction observables of p- and lower-sd-shell nuclei. As first application we concentrate on energy levels of the 9Be system for which all excited states lie above the n-8Be threshold. For all energy levels, the inclusion of the continuum significantly improves the agreement with experiment, which was an issue in standard no-core shell model calculations. Furthermore, we find the proper treatment of the continuum indispensable for reliable statements about the quality of the adopted 3N interaction from chiral effective field theory. In particular, we find the 1/2+ resonance energy, which is of astrophysical interest, in good agreement with experiment.