Electromagnetic moments of the odd-mass nickel isotopes $^{59-67}$Ni

TL;DR

This study measures magnetic and quadrupole moments of odd-mass nickel isotopes using laser spectroscopy and compares results with advanced ab initio and shell-model calculations, highlighting the importance of two-body currents.

Contribution

It demonstrates that including two-body-current contributions in VS-IMSRG calculations significantly improves agreement with experimental nuclear moments.

Findings

Two-body-current contributions reduce deviation from experimental moments by a factor of 3 to 5.

Largest contributions observed for isotopes with high angular momentum in f orbitals.

VS-IMSRG with two-body currents outperforms traditional shell-model calculations in the nickel region.

Abstract

The magnetic dipole and the spectroscopic quadrupole moments of the nuclear ground states in the odd-mass nickel isotopes $^{59-67}$Ni have been determined using collinear laser spectroscopy at the CERN-ISOLDE facility. They are compared to ab initio valence-space in-medium similarity renormalization group (VS-IMSRG) calculations including contributions of two-body currents as well as to shell-model calculations. The two-body-current contributions significantly improve the agreement with experimental data, reducing the mean-square deviation from the experimental moments by a factor of 3 to 5, depending on the employed interaction. For all interactions, the largest contributions are obtained for the $5/2^-$ ($7/2^-$) isotopes $^{65}$Ni ($^{55}$Ni), which is ascribed to the high angular momentum of the $f$ orbitals. Our results demonstrate that the inclusion of two-body-current contributions to the magnetic moment in an isotopic chain of complex nuclei can be handled by the VS-IMSRG and can outperform phenomenological shell-model calculations using effective $g$-factors in the nickel region.