Effect of nonflow and flow fluctuations on elliptic flow methods

TL;DR

This paper analyzes how flow fluctuations and nonflow effects influence elliptic flow measurements, providing equations to unify different methods' estimates under reasonable assumptions.

Contribution

It clarifies the relationship between various elliptic flow measurement methods and offers a way to reconcile their results through a unified framework.

Findings

Event-plane estimates lie between two- and multiparticle correlation methods.

Nonflow effects and fluctuations cannot be separated without additional assumptions.

Measured elliptic flow values can be unified into a single mean value under certain conditions.

Abstract

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 correlation 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.