On the necessity to include event-by-event fluctuations in experimental evaluation of elliptical flow

Elliptic flow at RHIC is computed event-by-event with NeXSPheRIO. We show that when symmetry of the particle distribution in relation to the reaction plane is assumed, as usually done in the experimental extraction of elliptic flow, there is a disagreement between the true and reconstructed elliptic flows (15-30% for $\eta$=0, 30% for $p_\perp$=0.5 GeV). We suggest a possible way to take into account the asymmetry and get good agreement between these elliptic flows.