  Recently it has been discovered that the elliptic flow, v2, of composite
charged particles emitted at midrapidity in Heavy-Ion collisions at
intermediate energies shows the strongest sensitivity to the Nuclear Equation
of State (EoS) which has been observed up to now within a microscopic model.
This dependence on the nuclear EoS is predicted by Quantum Molecular Dynamics
(QMD) calculations [1] which show as well that the absorption or rescattering
of in-plane emitted particles by the spectator matter is not the main reason
for the EoS dependence of the elliptic flow at mid-rapidity but different
density gradients (and therefore different forces) in the direction of the
impact parameter (x-direction) as compared to the direction perpendicular to
the reaction plan (y-direction), caused by the presence of the spectator
matter. The stronger density gradient in y-direction accelerates the particles
more and creates therefore a negative v2. When using a soft momentum dependent
EoS, the QMD calculations reproduce the experimental results.
