Coulomb energy difference as a probe of isospin-symmetry breaking in the upper fp-shell nuclei

TL;DR

This paper investigates the Coulomb energy differences in upper fp-shell nuclei, revealing isospin-symmetry breaking effects and explaining anomalies through large-scale shell-model calculations.

Contribution

It introduces a new computational approach using the Sakurai-Sugiura algorithm to accurately reproduce Coulomb energy differences in nuclei with A=66-78.

Findings

Reproduces experimental Coulomb energy differences accurately.

Explains negative CED at A=70 via neutron excitations and spin-orbit effects.

Highlights the role of cross-shell excitations in isospin-symmetry breaking.

Abstract

The anomaly in Coulomb energy differences (CED) between the isospin T=1 states in the odd-odd N=Z nucleus 70Br and the analogue states in its even-even partner 70Se has remained a puzzle. This is a direct manifestation of isospin-symmetry breaking in effective nuclear interactions. Here, we perform large-scale shell-model calculations for nuclei with A=66-78 using the new filter diagonalization method based on the Sakurai-Sugiura algorithm. The calculations reproduce well the experimental CED. The observed negative CED for A=70 are accounted for by the cross-shell neutron excitations from the fp-shell to the g9/2 intruder orbit with the enhanced electromagnetic spin-orbit contribution at this special nucleon number.