Representation of the constraints on the density dependence of symmetry energy (inset) and pressure as a function of the symmetry energy at saturation density in neutron matter. The hatched areas are extracted from recent analyses of nuclear collisions of Sn nuclei. Open rectangles and the symbol in the inset were obtained from the properties of individual nucleus.
EOS physics at FRIB
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SEP researchers and their colleagues at the National Superconducting Cyclotron Laboratory (NSCL) on the campus of Michigan State University have recently developed a consistent theoretical interpretation of a range of nucleus-nucleus collision data previously measured at the NSCL. The crosshatched region of the graph shows the allowed values for the symmetry energy and its contribution to pressure in pure neutron matter at saturation density.
The inset shows what this analysis implies about the density dependence of the symmetry energy. These graphs also show comparison of these results to other attempts to extract the symmetry energy from the properties of individual nuclei. A value for the symmetry energy at around 0.4 normal nuclear matter density, extracted from Giant Dipole Resonance (GDR) data, is indicated by the symbol in the inset. The open region in the main figure labeled “IAS” indicates the constraints obtained from analyses of the excitation energies of Isobaric Analog states, (IAS). The region labeled “PDR”, for Pygmy Dipole Resonance, results from analyses of low-lying electric dipole strength in neutron-rich nuclei. The region enclosed by the two diagonal lines labeled “Skin(Sn)” are the boundaries of recent constraints obtained from published skin thickness of tin nuclei.
Some shifts in the boundaries of the constrained regions can be expected with improvements in the precision of the experimental data and with the evolution of the theory. Nevertheless, the consistency among the different probes of the symmetry energy and the possibility of probing higher densities with nucleus-nucleus collisions at higher energies suggests that the symmetry energy will soon be constrained over a range of densities.