Investigation of the nuclear mean field by precision measurements of the spectator response to the participants blast

The longitudinal re-acceleration phenomenon of the fragmentation residues, as found recently in projectile fragmentation of uranium [1,2], has been interpreted [3] as the postulated spectator response to the participants’ blast [4]. According to transport calculations, the longitudinal momenta of the surviving residues yield a direct access to the momentum-dependent properties of the nuclear mean field (MF), little affected by the uncertainties in nuclear incompressibility [4]. Therefore, we propose an experiment in which the more detailed investigation of the re-acceleration phenomenon will be performed. We plan to explore the reacceleration dependence on the initial beam energy as well as the importance of the isospin effects on the evolution and strength of the participants blast, thus directly addressing the characteristics of the momentum dependent MF. We propose to measure longitudinal momenta of the final residues in the systems of Au+Au at 250, 500, 750 and 1000 A MeV, Sn+Sn and Sn+Sn at 1000 A MeV at the Fragment Separator (FRS), GSI Darmstadt.