Constraints on the density dependence of the symmetry energy from heavy-ion collisions

Constraints on the equation of state (EoS) for symmetric matter (equal neutron and proton numbers) have been extracted from energetic collisions of heavy ions over a range of energies. Collisions of neutron-deficient and neutron-rich heavy ions now provide initial constraints on the EoS of neutron-rich matter at subsaturation densities from isospin diffusions and neutron proton ratios. This article reviews the experimental constraints on the density dependence of symmetry energy at subsaturation density.