Probing the isospin dependence of the in-medium nucleon-nucleon cross sections with radioactive beams

Within a transport model we search for potential probes of the isospin dependence of the in-medium nucleon-nucleon (NN ) cross sections. Traditional measures of the nuclear stopping power are found to be sensitive to the magnitude but they are ambiguous for determining the isospin dependence of the in-medium NN cross sections. It is shown that isospin tracers, such as the neutron/proton ratio of free nucleons, at backward rapidities and angles in nuclear reactions induced by radioactive beams in inverse kinematics are a sensitive probe of the isospin dependence of the in-medium NN cross sections. At forward rapidities and angles, in contrast, they are more sensitive to the density dependence of the symmetry energy. Measurements of the rapidity and angular dependence of the isospin transport in nuclear reactions will enable a better understanding of the isospin dependence of in-medium nuclear effective interactions.