Symmetry energy from elliptic flow in 197Au + 197Au
  The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. The results obtained from the existing FOPI/LAND data for 197Au + 197Au collisions at 400 MeV/nucleon in comparison with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to rho/rho_0^gamma with gamma = 0.9 +- 0.4. 
P. Russotto, P.Z. Wu, M. Zoric, M. Chartier, Y. Leifels, R.C. Lemmon,   Q. Li, J. Lukasik, A. Pagano, P. Pawlowski, W. Trautmann
nucl-ex