Publication : t09/106

Abstract:
The second and fourth Fourier harmonic of the azimuthal distribution of particles, v_2 and v_4, have been measured in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The ratio v_4/(v_2)^2 is significantly larger than predicted by hydrodynamics. Effects of partial thermalization are estimated on the basis of a transport calculation, and are shown to increase v_4/(v_2)^2 by a small amount. We argue that the large value of v_4/(v_2)^2 seen experimentally is mostly due to elliptic flow fluctations. However, the standard model of eccentricity fluctuations is unable to explain the large magnitude of v_4/(v_2)^2 in central collisions.

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