Transport properties of isospin effective mass splitting

We investigate in detail the momentum dependence (MD) of the effective in medium nucleon-nucleon (NN) interaction in the isovector channel. We focus the discussion on transport properties of the expected neutron-proton (n/p) effective mass splitting at high isospin density. We look at observable effects from collective flows in heavy ion collisions (HIC) of charge asymmetric nuclei at intermediate energies. Using microscopic kinetic equation simulations nucleon transverse and elliptic collective flows in Au + An collisions are evaluated. In spite of the reduced charge asymmetry of the interacting system interesting isospin-MD effects are revealed. Good observables, particularly sensitive to the n/p mass splitting, appear to be the differences between neutron and proton flows. The importance of more exclusive measurements, with a selection of different bins of the transverse momenta (p(t)) of the emitted particles, is stressed. In more inclusive data a compensation can be expected from different p(t)-contributions, due to the microscopic isospin-MD structure of the nuclear mean field in asymmetric matter. (C) 2003 Elsevier B.V. All rights reserved.