The symmetry energy from heavy ion reactions

Wolfgang Trautmann
2010 Proceedings of XLVIII International Winter Meeting on Nuclear Physics in Memoriam of Ileana Iori — PoS(BORMIO2010)   unpublished
The equation of state of asymmetric nuclear matter is an essential ingredient in nuclear physics and astrophysics but, as of today, insufficiently constrained by experiment. The symmetry energy, i.e. the difference between the energy of neutron matter and of symmetric matter, and its dependence on density are important for the modelling of neutron stars and supernova explosions as well as for isospin phenomena in nuclear reactions and nuclear structure. Heavy-ion reactions are a unique tool for
more » ... obtaining information on the symmetry energy in the laboratory, and a considerable activity is presently devoted to its behavior at sub-and supra-saturation density. In this contribution, new results are presented which were obtained in experiments conducted at the GSI laboratory with relativistic heavy-ion beams. A systematic study of isotopic effects in spectator fragmentation was performed at the ALADIN spectrometer with 124 Sn primary and 107 Sn and 124 La secondary beams of 600 MeV/nucleon incident energy. The analysis within the Statistical Fragmentation Model shows that the symmetry-term coefficient entering the liquiddrop description of the emerging fragments decreases significantly as the multiplicity of fragments and light particles from the disintegration of the produced spectator systems increases. Higher densities were probed in the FOPI/LAND study of nucleon and light-particle flows in central and mid-peripheral collisions of 197 Au+ 197 Au nuclei at 400 MeV/nucleon incident energy. From the comparison of the measured neutron and hydrogen squeeze-out ratios with predictions of the UrQMD model a moderately soft symmetry term with a density dependence of the potential term proportional to (ρ/ρ 0 ) γ with γ = 0.9 ± 0.3 is favored.
doi:10.22323/1.103.0061 fatcat:bcmbccc2ajdp3irdcluuabt4pq