Constraining The Symmetry Energy (Far) Above Saturation Density Using Elliptic Flow

A QMD transport model that employs a modified momentum dependent interaction (MDI2) potential, supplemented by a phase-space coalescence model fitted to experimental multiplicities of free nucleons and light clusters, is used to study the density dependence of the symmetry energy above the saturation point by a comparison with experimental elliptic flow ratios measured by the FOPI-LAND and ASYEOS collaborations for 197Au+197Au collisions at 400 MeV/nucleon impact energy. Comparing theoretical predictions with experimental data for neutron-to-proton and neutron-to-charged particles elliptic flow ratios the following constraint is extracted for the slope L and curvature Ksym of symmetry energy at saturation: L=59±24(exp)±16(th)±10(sys) MeV and Ksym=0±370(exp)±220(th)±150(sys) MeV. Theoretical errors are the result of poorer known model ingredients. Systematical uncertainties are generated by the inability of the transport model to reproduce experimental light-cluster-to-proton multiplicity ratios. A more accurate value for L, free of systematical theoretical uncertainties, can be extracted from the neutron-to-proton elliptic flow ratio alone: L=63±18(exp)±14(th) MeV