Strong compression effects in fast nuclear collisions

The importance of the impact parameter for compression effects and the reaction mechanism in high energy heavy ion collisions (HEHIC) are investigated within three-dimensional nuclear fluid dynamics. For central collisions of a small projectile (Ne) with a heavy target (U) a Mach shock wave is formed resulting in the sidewards emission of matter with azimuthally symmetric fragment distribution. At intermediate impact parameters the Highly-Inelastic Bounce-Off (HIBO) appears, where the large compression potential leads to the sidewards deflection of the projectile, which then explodes. A large collective transverse momentum transfer to the target leads to azimuthally asymmetric (180° correlated) fragment distributions. The deflection angles, energy losses, mean associated multiplicities as well as the maximum compression and thermal excitation of the system are calculated as a function of the impact parameter. A characteristic deflection function is obtained which may be used to determine the impact parameter in HEHI collisions experimentally. The influence of the nuclear equation of state is discussed. The strongly differing results of central reactions and those at intermediate impact parameter seem to have been observed in preliminary data of the GSI-Marburg-LBL collaboration. This is viewed as further indication for the occurrence of strong compression phenomena in nucleus-nucleus collisions of high energy.