Transverse velocity scaling in Au+Au midrapidity emissions

The emission of intermediate-mass fragments in collisions of 197Au on 197Au was systematically studied over the range of incident energies from 40 to 150 A MeV using the 4π-multidetector INDRA and beams from the heavy-ion synchrotron SIS at GSI Darmstadt. The analysis was performed as a function of incident energy and of impact parameter, defined through the total transverse energy of light charged particles (Etrans 12, Z≤2). This observable was found to scale linearly with the collision energy up to a certain limit above which it saturates. Strong forward-backward asymmetries in the emission pattern with respect to the rapidities of the projectile and target residua were observed. Their possible relation to equilibration is discussed and interpreted in the framework of molecular dynamics and statistical multifragmentation models. Transverse velocities at midrapidity for peripheral collisions were found to show a surprisingly weak dependence on the incident energy. On the contrary, transverse velocities at midrapidity for central collisions showed a strong dependence on incident energy indicating an increasing importance of collective flow with increasing bombarding energy