Anisotropic flow in ultra-relativistic heavy-ion collisions

The sign reversal of the directed flow parameter v(1) in the central rapidity region in Au + Au collisions at roots = 200 A GeV is studied within the Ultra-relativistic Quantum Molecular Dynamics Model. This anti-flow is shown to be linked to the expansion of the hot matter created. In line with this observation the predicted elliptic flow parameter v(2) of various particle species is linked to the mean free path of these particles. (C) 2002 Elsevier Science B.V. All rights reserved.