Candidate toroidal electric dipole mode in the spherical nucleus $^{58}$Ni

TL;DR

This paper reports the first experimental identification of candidate toroidal dipole modes in the nucleus $^{58}$Ni, using high-resolution scattering experiments, and highlights the importance of transverse electron scattering form factors as evidence.

Contribution

It provides the first experimental evidence for toroidal dipole excitations in a nucleus, demonstrating the relevance of electron scattering form factors for their identification.

Findings

Candidates for toroidal dipole modes identified in $^{58}$Ni

Transverse electron scattering form factors are effective observables

First experimental evidence of nuclear toroidal modes

Abstract

Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus $^{58}$Ni and demonstrate that transverse electron scattering form factors represent a relevant experimental observable to prove their nature.