Elliptic flow analysis in Au plus Au collisions at √sNN=200 GeV:: Fluctuations vs non-flow effects -: art. no. 064911

The cumulant method is applied to study elliptic flow (v(2)) in Au+Au collisions at root s = 200A GeV, with the UrQMD model. In this approach, the true event plane is known and both the nonflow effects and event-by-event spatial (epsilon) and v(2) fluctuations exist. Qualitatively, the hierarchy of v(2)s from two-, four-, and six-particle cumulants is consistent with the STAR data; however, the magnitude of v(2) in the UrQMD model is only 60% of the data. We find that the four- and six-particle cumulants are good measures of the real elliptic flow over a wide range of centralities except for the most central and very peripheral events. There the cumulant method is affected by the v(2) fluctuations. In midcentral collisions, the four- and six-particle cumulants are shown to give a good estimation of the true differential v(2), especially at large transverse momentum, where the two-particle cumulant method is heavily affected by the nonflow effects.