Transport properties of isospin effective mass splitting

Abstract

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 $Au+Au$ 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.Comment: 18 pages, 11 figure