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

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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.