Comparing symmetry energy predictions and recent constraints from the ASY-EOS experiment at GSI

Abstract

Predictions for the interaction part of the symmetry energy obtained from microscopic approaches based upon different foundations are reviewed and discussed in the light of recent updated constraints obtained from reaction observables in the ASY-EOS experiment at GSI. The discussion is then extended to the neutron skin thickness in 208 Pb and its relation to the density derivatives of the symmetry energy at and below saturation density. With regard to the latter, the main point is to demonstrate the importance of proper consideration of the theoretical uncertainties of microscopic predictions in order to guide phenomenological analyses.

Analysis of the neutron matter equation of state and the symmetry energy up to fourth order of chiral effective field theory

“…In the past, we have expressed concerns (see, for instance, Ref. [77]), about some aspects of the methodologies utilized to extract symmetry energy constraints around saturation density from measured observables, in particular about the degree of model dependence of the constraints, which do not provide a functional relation between density and symmetry energy. Hopefully, a different approach to the analyses will reduce the model dependence and the discrepancies among the constraints given at saturation density.…”

Fock contributions to nuclear symmetry energy and its slope parameter based on Lorentz-covariant decomposition of nucleon self-energies

“…which has been often used in the analyses in Refs [60,61]. Using this function, in Table V, we provide the γ parameter in E sym , which is chosen so as to reproduce the result of each model.…”

“…Recent experimental analyses on the density dependence of E sym have been performed by using the free Fermi Gas model, in which E sym can be separated into the kinetic and potential terms as E sym (ρ B ) = E kin sym (ρ B ) + E pot sym (ρ B ), where ρ B is the total baryon density [14,[60][61][62][63]. In this decomposition, E kin sym is expressed in terms of only the degrees of freedom of nucleons, and it is typically parametrized as E kin sym (ρ 0 )(ρ B /ρ 0 ) 2/3 , where E kin sym (ρ 0 ) is the symmetryenergy value at ρ 0 .…”