Influence of Shear Viscosity of Quark-Gluon Plasma on Elliptic Flow in Ultrarelativistic Heavy-Ion Collisions

We investigate the influence of a temperature-dependent shear viscosity over entropy density ratio $\eta /s$ on the transverse momentum spectra and elliptic flow of hadrons in ultrarelativistic heavy-ion collisions. We find that the elliptic flow in $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the viscosity of the quark-gluon plasma (QGP). At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity.

Figure 1

Different parametrizations of $\eta /s$ as a function of temperature. The ($LH\mathrm{\text{−}}LQ$) line is shifted downwards and the ($HH\mathrm{\text{−}}HQ$) line upwards for better visibility.

Figure 2

Transverse momentum spectra of positive pions in the 0%–5% most central collisions and elliptic flow coefficients in the 20%–30% centrality class at RHIC and LHC. Different curves correspond to the different parametrizations of the temperature dependence of $\eta /s$. Data in panel (a) are from Ref. 15 and in panels (d) and (e) from Refs. 27, 28.

Figure 3

Same as Fig. 2d, but for elliptic flow of thermal (i.e., without decays) pions with $\delta f=0$.