Quantitative and Conceptual Considerations for Extracting the Knudsen Number in Heavy Ion Collisions

Abstract

In this paper we examine the methodology for extracting the Knudsen number (K) and the ratio of shear viscosity to entropy density (eta/s) developed by Drescher et al. The final result for eta/s turns out to be quite sensitive to Glauber parameters, and particularly the parameter x which controls the balance between Npart and Ncoll. We also explore how alternative formulations of the functional relation between the elliptic flow and Knudsen number impacts the physics conclusions, based on Pade approximants. Finally, we extend the calculation to include a limiting minimum value on the mean free path proportional to the DeBroglie wavelength. These results emphasize the importance of clarifying the initial state used in different calculations, as well as the ambiguities inherent in using a transport approach in a strongly-coupled regime.

11 pages, 6 figures, submitted for refereed publication

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• Dissecting the role of initial collision geometry for jet quenching observables in relativistic heavy ion collisions
• Quark-Gluon Plasma at RHIC and the LHC: Perfect Fluid too Perfect?
• Dynamics of pion production in heavy-ion collisions around 1A GeV energies
• Phenomenology of the little bang
• Theoretical Modeling of J/psi Yield Modifications in Proton (Deuteron) - Nucleus Collisions at High Energy
• Imprints of Nuclear Symmetry Energy on Properties of Neutron Stars
• Nuclear symmetry energy and proton-rich reactions at intermediate energies
• Puzzles, Progress, Prospects: pre-Summary for the Quark Matter 2009 Conference
• Causal dissipative hydrodynamics for heavy ion collisions