Is the quark gluon plasma produced in RHIC collisions strongly coupled?

Abstract

Recent hexadecapole (v4) and elliptic (v2) flow measurements are used to constrain estimates for the degree of local equilibrium, mean free path $\lambda$, and the viscosity to entropy density ratio (eta/s) of the plasma produced in Au+Au collisions at RootS = 200 GeV. The eccentricity-scaled flow coefficients v2/e2 and v4/e4 indicate that the plasma achieves a degree of local equilibrium within 5 - 10% of the value expected for a fluid with eta/s equal to the conjectured lower bound of 1/4pi. Estimates for $\lambda$ and eta/s as a function of collision centrality and particle transverse momentum pT, points to transverse expansion dynamics compatible with a strongly coupled low viscosity plasma.

Comments: Proceedings of the 25th Winter Workshop on Nuclear Dynamics, Big Sky, Montana, February 1--8, 2009