Directed flow at mid-rapidity in event-by-event hydrodynamics

Understand

Fluctuations in the initial geometry of a nucleus-nucleus collision have been recently shown to result in a new type of directed flow (v_1) that, unlike the usual directed flow, is also present at midrapidity.

• We compute this new v_1 versus transverse momentum and centrality for Au-Au collisions at RHIC using the hydrodynamic code NeXSPheRIO.
• We find that the event plane of v_1 is correlated with the angle of the initial dipole of the distribution, as predicted, though with a large dispersion.
• It is uncorrelated with the reaction plane.