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arXiv · 1803.02072

Nearly isentropic flow at sizeable $η/s$

Aleksi Kurkela·Urs Achim Wiedemann·Bin Wu
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Abstract

Non-linearities in the harmonic spectra of hadron-nucleus and nucleus-nucleus collisions provide evidence for the dynamical response to azimuthal spatial eccentricities. Here, we demonstrate within the framework of transport theory that even the mildest interaction correction to a picture of free-streaming particle distributions, namely the inclusion of one perturbatively weak interaction ("one-hit dynamics"), will generically give rise to all observed linear and non-linear structures. We further argue that transport theory naturally accounts within the range of its validity for realistic signal sizes of the linear and non-linear response coefficients observed in azimuthal momentum anisotropies with a large mean free path of the order of the system size in peripheral ($\sim 50 \%$ centrality) PbPb or central pPb collisions. The shear viscosity to entropy density ratio $η/s$ of such a transport theory is approximately an order of magnitude larger than that of an almost perfect fluid. The phenomenological success of transport simulations thus challenges the perfect fluid paradigm of ultra-relativistic nucleus-nucleus and hadron-nucleus collisions.

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Aleksi Kurkela, Urs Achim Wiedemann, Bin Wu. 2018-07-06. Nearly isentropic flow at sizeable $η/s$. https://doi.org/10.1016/j.physletb.2018.06.064

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