Prof. Paweł Danielewicz, Michigan State University, USA

Symmetry energy from isobaric analog states

Symmetry energy describes how the net nuclear energy changes with changing neutron-proton asymmetry. Knowledge of the symmetry energy, and especially its dependence on density, is needed for extrapolating from nuclei to matter in neutron stars. Charge invariance of nuclear interactions can be used to demonstrate that nuclei can be assigned nuclear symmetry coefficients that depend on mass and reflect changes of symmetry energy with density, within nuclear surface. Those coefficients are extracted nucleus-by-nucleus from excitation energies to isobaric analog states. The variation of those coefficients with mass is then used to constrain the density dependence of symmetry energy. As nuclear ground states minimize energy, neutrons and protons displace relative to each other to minimize symmetry energy contribution to the net energy. Universality of the features of neutron and proton distributions, in the context of symmetry energy, is discussed.