Directed flow at midrapidity in heavy-ion collisions

Abstract

It was recently shown that fluctuations in the initial geometry of a heavy ion collision generally result in a dipole asymmetry of the distribution of outgoing particles. This asymmetry, unlike the usual directed flow, is expected to be present at a wide range of rapidity -- including midrapidity. First evidence of this phenomenon can be seen in recent two-particle correlation data by STAR, providing the last element necessary to quantitatively describe long-range dihadron correlations. We extract differential directed flow from these data and propose a new direct measurement.

4 pages, 1 figure; v3: fixed factors of 2 in Eqs. 3,4; v2: a number of minor improvements, version accepted for publication in PRL