We discuss how the different estimates of elliptic flow are influenced by flow fluctuations and nonflow effects. It is explained why the event-plane method yields estimates between the two-particle correlation methods and the multiparticle correlatio
n methods. It is argued that nonflow effects and fluctuations cannot be disentangled without other assumptions. However, we provide equations where, with reasonable assumptions about fluctuations and nonflow, all measured values of elliptic flow converge to a unique mean elliptic flow in the participant plane. Thus, the 20% spread in observed elliptic flow measurements from different analysis methods is no longer mysterious.
We discuss how the different estimates of elliptic flow are influenced by flow fluctuations and nonflow effects. It is explained why the event-plane method yields estimates between the two-particle correlation methods and the multiparticle correlatio
n methods. It is argued that nonflow effects and fluctuations cannot be disentangled without other assumptions. However, we provide equations where, with reasonable assumptions about fluctuations and nonflow, all measured values of elliptic flow converge to a unique mean v_{2,PP} elliptic flow in the participant plane and, with a Gaussian assumption on eccentricity fluctuations, can be converted to the mean v_{2,RP} in the reaction plane. Thus, the 20% spread in observed elliptic flow measurements from different analysis methods is no longer mysterious.
Recent developments in the field of anisotropic flow in nuclear collision are reviewed. The results from the top AGS energy to the top RHIC energy are discussed with emphasis on techniques, interpretation, and uncertainties in the measurements.
