Elliptic flow in heavy-ion collisions near the balance energy

The proton elliptic flow in collisions of Ca-48 on Ca-48 at energies from 3 0 to 100 MeV/nucleon is studied in an isospin-dependent transport model. Wi th increasing incident energy, the elliptic flow shows a transition from po sitive to negative flow. Its magnitude depends on both the nuclear equation of state (EOS) and the nucleon-nucleon scattering cross section. Different elliptic flows are obtained for a stiff EOS with free nucleon-nucleon cros s sections and a soft EOS with reduced nucleon-nucleon cross sections, alth ough both lead to vanishing in-plane transverse flow at the same balance en ergy.