Momentum--dependent nuclear mean fields and collective flow in heavy ion collisions

We use the Boltzmann-Uehling-Uhlenbeck model to simulate the dynamical evolution of heavy ion collisions and to compare the effects of two parametrizations of the momentum--dependent nuclear mean field that have identical properties in cold nuclear matter. We compare with recent data on nuclear flow, as characterized by transverse momentum distributions and flow ($F$) variables for symmetric and asymmetric systems. We find that the precise functional dependence of the nuclear mean field on the particle momentum is important. With our approach, we also confirm that the difference between symmetric and asymmetric systems can be used to pin down the density and momentum dependence of the nuclear self consistent one--body potential, independently. All the data can be reproduced very well with a momentum--dependent interaction with compressibility K = 210 MeV.Comment: 15 pages in ReVTeX 3.0; 12 postscript figures uuencoded; McGill/94-1