Nearly isentropic flow at sizeable η/s

Aleksi Kurkela,Urs Achim Wiedemann,Bin Wu

doi:10.1016/j.physletb.2018.06.064

Aleksi Kurkela, Urs Achim Wiedemann + Show 1 more

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https://doi.org/10.1016/j.physletb.2018.06.064

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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 (∼50% centrality) PbPb or central pPb collisions. As a non-vanishing mean free path is indicative of non-minimal dissipation, this challenges the perfect fluid paradigm of ultra-relativistic nucleus–nucleus and hadron–nucleus collisions.

Highlights

The applicability of relativistic transport theory ranges from the description of free-streaming particle distributions via weakly interacting systems of long mean free path up to systems exhibiting viscous fluid dynamic behavior
Fluid dynamic simulations of ultra-relativitic heavy ion collisions at RHIC and at the LHC can account for hadronic spectra in nucleus-nucleus collisions, their azimuthal anisotropies vm, their pT differential hadrochemical composition, as well as for correlations between different vm’s, see Refs. [9, 10] for recent reviews
These fluid dynamic simulations favor an almost perfect fluid with a very small ratio of shear viscosity to entropy density η/s ∼ O(1/4π), suggesting that the system is so strongly interacting that the notion of quasi-particles and mean free path becomes doubtful since no particle excitation propagates over distances larger than O(1/T )

Summary

Introduction

The applicability of relativistic transport theory ranges from the description of free-streaming particle distributions via weakly interacting systems of long mean free path up to systems exhibiting viscous fluid dynamic behavior. We want to investigate how azimuthal anisotropies vm in the transverse flow of energy density and non-linear correlations between these vm’s arise in transport theory (2) for large mean free path lmfp (i.e. small γ).

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