Anisotropic flow in ultra-relativistic heavy ion collisions

A sign reversal of the directed flow parameter v1 in the central rapidity region in Au+Au collisions at √ s = 200 AGeV is predicted. 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 v2 of various particle species is linked to the mean free path of these particles. LBNL-preprint: LBNL-46096 Typeset using REVTEX ξ Feodor Lynen Fellow of the Alexander v. Humboldt Foundation ∗E-mail: [email protected] 1 The exploration of the transverse collective flow is the earliest predicted observable to probe heated and compressed nuclear matter [1]. Its sensitivity to the equation of state (EoS) might be used to search for abnormal matter states and phase transitions [2–4]. Until now, the study of directed and anisotropic flow in high energy nuclear collisions is attracting large attention from both experimentalists and theorists [5–9]. Flow in general is sensitive to the equation of state [5,6,10–12] which governs the evolution of the system created in the nuclear collision. Elliptical flow [10,13–20] (i.e. squeeze-out except for a reversed sign in the observable) is especially sensitive to the early time scales of the reaction. It might serve as a keyhole to the (non-)equilibrium dynamics of the strongly interacting matter even before hadronization. In fluid dynamics, the transverse collective flow is intimately connected to the pressure P (ρ, S) (which in turn depends on the density ρ and the entropy S) of the matter in the reaction zone [21]: