Figure 8

$v_{4}[2]$ with different $|\Delta\eta|$ gaps is presented in Pb--Pb collisions at $\sqrt{s_{_{\rm NN}}} = 2.76$~TeV. $v_{4}[2, |\Delta\eta|> 0]$, $v_{4}[2, |\Delta\eta|> 0.4]$, and $v_{4}[2, |\Delta\eta|> 0.8]$ are represented by circles, diamonds, and squares, respectively. The different panels show the centrality evolution of the measurements Hydrodynamic calculations with MC-Glauber initial conditions and $\eta/s =$ 0.08~ and with MC-KLN initial conditions and $\eta/s =$ 0.20~, with Trento initial conditions and temperature dependent $\eta/s$~ and AMPT initial conditions and $\eta/s =$ 0.08~ are shown in green dot-dash, orange dashed curves, and magenta and grey shaded areas, respectively.
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