Probing Nuclear Equation of State with Heavy Ion Collisions*

The equation of state (EOS) is a fundamental property of nuclear matter, important for studying the structure of systems as diverse as the atomic nucleus and neutron stars. Understanding the physics of neutron stars is becoming even more important recently because of the observation of gravitational waves from the neutron star merger. 
Nuclear reactions involving heavy-ion collisions in the laboratories can produce the nuclear matter similar to those contained in neutron stars. The density and momentum dependence of the EOS of asymmetric nuclear matter, especially the symmetry energy term, is widely unconstrained. Collisions of neutron-deficient and neutron-rich heavy ions studied in the laboratory already provide initial constraints on the EoS of neutron-rich matter at sub-saturation densities. 
Finding appropriate constraints, especially at higher densities, requires new experimental measurements as well as advances in theoretical understanding of nuclear collisions and neutron stars.We will review the latest progress in constraining the density and momentum dependence of nuclear symmetry energy and discuss their relevance to astrophysics, in particular neutron star mergers.