Anisotropic Flow at the Relativistic Heavy Ion Collider

Anisotropic flow is recognized as one of the main observables providing information on the early stage of a heavy-ion collision. At RHIC the observed strong collective flow of the bulk matter is considered evidence for an early onset of thermalization, and an ideal hydrodynamical expansion with an equation of state consistent with that obtained from lattice QCD calculations. The large collective flow of the bulk and the inferred large energy loss of the produced jets propagating through the created matter are key signatures for the formation of a Quark Gluon Plasma.