Quadrupole moments and proton-neutron structure in p-shell mirror nuclei

TL;DR

This paper uses ab initio calculations to analyze proton and neutron quadrupole moments in p-shell mirror nuclei, providing insights into nuclear deformation and isospin symmetry with a focus on the challenges of convergence.

Contribution

It introduces a robust method for comparing quadrupole moments in mirror nuclei using ab initio calculations, addressing convergence issues and symmetry tests.

Findings

Predictions for mirror quadrupole moments generally agree with experimental data.

Isospin symmetry holds approximately for quadrupole moments across mirror pairs.

Ratios of quadrupole moments are more reliably converged than individual moments.

Abstract

Electric quadrupole (E2) matrix elements provide a measure of nuclear deformation and related collective structure. Ground-state quadrupole moments in particular are known to high precision in many p-shell nuclei. While the experimental electric quadrupole moment only measures the proton distribution, both proton and neutron quadrupole moments are needed to probe proton-neutron asymmetry in the nuclear deformation. We seek insight into the relation between these moments through the ab initio no-core configuration interaction (NCCI), or no-core shell model (NCSM), approach. Converged ab initio calculations for quadrupole moments are particularly challenging, due to sensitivity to long-range behavior of the wave functions. We therefore study more robustly-converged ratios of quadrupole moments: across mirror nuclides, or of proton and neutron quadrupole moments within the same nuclide. In calculations for mirror pairs in the p shell, we explore how well the predictions for mirror quadrupole moments agree with experiment and how well isospin (mirror) symmetry holds for quadrupole moments across a mirror pair.