Constraints on neutron skin thickness and symmetry energy

The structure of exotic neutron-rich nuclei is one of the main science drivers in contemporary nuclear physics research. The new measurements of pygmy dipole (PDR) and giant dipole (GDR) resonances in neutron-rich nuclei have sparked advancements in nuclear models. The quasiparticle random phase approximation, utilising the self-consistent mean-field derived from Skyrme effective interactions, is a widely used tool for describing the PDR and GDR. This approach made it possible to a successful description of the properties of low-lying states and the characteristics of giant multipole resonances in spherical nuclei, such the photoabsorption cross section. In this context, special attention is drawn to the electric dipole polarisability, which is associated with the total cross section in the GDR region. The electric dipole polarisability plays an important role in nuclear astrophysics, ranging from the nuclear structure to neutron stars.

Due to the anharmonicity of vibrations there is a coupling between simple particle-hole configurations and more complex states. As an illustration, we study the impact of complex configurations on the electric dipole polarisability in the neutron-rich Ca, Ni and Sn isotopes. The correlations between the neutron skin thickness, the electric dipole polarisability, the symmetry energy and its slope are studied. The analysis of experimental data and calculation results constrained the symmetry energy of nuclear matter in the range J=30-37 MeV.