ELLIPTIC FLOW FLUCTUATIONS IN AU+AU COLLISIONS AT $\sqrt{s_{NN}} = 200\, {\rm GeV}$

Abstract

This paper presents a measurement of event-by-event fluctuations of charged particle elliptic flow in Au + Au collisions at [Formula: see text] as a function of collision centrality. The relative non-statistical fluctuations of the elliptic flow coefficient, v2, are found to be approximately 40%. The magnitude of the observed relative fluctuations in v2 agrees with predictions based on spatial fluctuations of the participating nucleons in the initial nuclear overlap region. These results are consistent with a scenario where v2 is directly proportional to the eccentricity of the initial matter distribution on an event-by-event basis. The subsequent evolution of the system does not change this in any measurable way, consistent with hydrodynamic evolution with a very low viscosity. The agreement of the results with event-by-event eccentricity calculations indicates that matter in the initial stage of the collision is produced with a transverse granularity similar to that of the participant nucleons.