Abstract
We have employed a relativistic kinetic transport approach that incorporates initial state fluctuations to study the effect of a temperature dependent shear viscosity to entropy density ratio η / s ( T ) on the build-up of the anisotropic flows υ n ( p T ). We find that at LHC energies and for ultra-central collisions (0 – 0.2%) the υ n ( p T ) have a stronger sensitivity to the T dependence of η / s in the QGP phase and this sensitivity increases with the order of the harmonic n. Moreover we have studied the correlation between the initial spatial anisotropies ϵ n and the final flow coefficients 〈 υ n 〉 for different centralities and for the two beam energies. The study shows that at LHC energies there is more correlation than at RHIC energies. In particular at LHC energies and for ultra-central collisions the linear correlation coefficient C ( ϵ n , υ n ) ≈ 1 for n = 2, 3, 4 and 5 suggesting that the 〈 υ n 〉 are strongly related to the initial value of ϵ n .
Highlights
One of the most surprising results obtained in the experiments conducted at RHIC and more recently at the LHC is that the matter created in these heavy ion collisions behaves as an almost perfect fluid with a very low η/s ratio
We have studied the effect of the η/s on the anisotropic flows vn(pT ) for n = 2, 3, 4 and 5 within an event-by-event transport approach
We found that at LHC energies and for mid-peripheral collisions there is a weak sensitivity of vn(pT ) to the T dependence in the QGP phase
Summary
One of the most surprising results obtained in the experiments conducted at RHIC and more recently at the LHC is that the matter created in these heavy ion collisions behaves as an almost perfect fluid with a very low η/s ratio. The comparison between experimental data and theoretical calculations within viscous hydrodynamics and transport approach [1,2,3,4] have shown that this large value of v2 is consistent with a very low η/s. The comparison between experimental data and event-by-event viscous hydrodynamic calculations have shown that the expected range of viscosity explored from RHIC to LHC energies is about 4π η/s ∼ 1 − 3 [8, 9].
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