Abstract :
The complementary aspects of the strength of the symmetry energy at nuclear densities below and above saturation are illustrated with recent results from experiments performed 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 124Sn primary and 107Sn and 124La secondary beams of 600 MeV/nucleon incident energy. The analysis within the Statistical Fragmentation Model reveals that the symmetry-term coefficient entering the liquid-drop description of the emerging fragments decreases significantly as the disintegration of the spectator system into fragments and light particles increases. Higher densities were probed in more central collisions of 197Au + 197Au nuclei at 400 MeV/nucleon. The results obtained from the analysis of the FOPI/LAND experimental data on neutron and hydrogen squeeze-out in comparison with UrQMD model predictions favor a moderately soft symmetry term with a density dependence of the potential term proportional to γ(ρ/ρ0) with γ=0.9±0.3.
