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.

The electric dipole strength distribution in Ni 58 between 6 and 20 MeV has been determined from proton inelastic scattering experiments at very forward angles at RCNP, Osaka. The experimental data are rather well reproduced by quasiparticle random-phase approximation calculations including vibration coupling, despite a mild dependence on the adopted Skyrme interaction. They allow an estimate of the experimentally inaccessible high-energy contribution above 20 MeV, leading to an electric dipole polarizability α D ( Ni 58 ) = 3.48 ( 31 ) fm 3 . This serves as a test case for recent extensions of coupled-cluster calculations with chiral effective field theory interactions to nuclei with two nucleons on top of a closed-shell system.

Background: Electric and magnetic dipole strengths in nuclei at excitation energies well below the giant resonance region are of interest for a variety of nuclear structure problems including a possible electric dipole toroidal mode or the quenching of spin-isospin flip modes.

We present the design, developments, and test results of the new scintillating fiber based tracking detectors which are part of the R $$^3$$ 3 B experimental setup at GSI and FAIR, Darmstadt, Germany. Those tracking detectors are capable to track heavy ions of all charges at relativistic energies. Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible.