Multipolarity of the 9.529 MeV transition in 58Ni is unclear

Ascertain whether the 9.529 MeV transition in 58Ni corresponds to an electric-dipole (E1) excitation, a magnetic-dipole (M1) excitation, or an unresolved E1/M1 doublet by reconciling the inconsistent assignments across inelastic proton scattering, electron scattering, and photon scattering data sets.

Background

The authors compare transitions observed in (p,p′), (e,e′), and (γ,γ′) experiments. For the state around 9.53 MeV, photon scattering data indicate unambiguous E1 character, while charge-exchange comparisons suggested a possible analog M1 excitation, raising the possibility that the observed strength may be an unresolved doublet.

Because no M1 signal is seen in the photon scattering experiments, the authors assume E1 dominance for their analysis, but they explicitly note the assignment remains unclear, making this specific state a target for further investigation using complementary probes or improved resolution.

References

However, there is an unclear assignment already noted in Ref. with respect to the state seen at 9.529 MeV in the present experiment with corresponding states at 9.513 MeV in $(e,e\prime)$ and at 9.523 MeV in $(\gamma,\gamma\prime)$.

— Electric and magnetic dipole strength in $^{58}$Ni from forward-angle inelastic proton scattering (2404.15906 - Brandherm et al., 24 Apr 2024) in Section 4.1 (Results and comparison with other experiments)