Abstract
Anisotropic flow coefficients, vn, non-linear flow mode coefficients, χn,mk, and correlations among different symmetry planes, ρn,mk are measured in Pb-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 < pT< 5.0 GeV/c within the pseudorapidity interval 0.4 < |η| < 0.8 as a function of collision centrality. The vn coefficients and χn,mk and ρn,mk are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system.
Highlights
Where the curly brackets denote the average over the transverse plane, i.e. {· · · } = dxdy e(x, y, τ0)(· · · ), r is the distance to the system’s center of mass, φ is the azimuthal angle, e(x, y, τ0) is the energy density at the initial time τ0, and Φn is the participant plane angle, defining the spatial symmetry of the nuclear constituents in the participant region
Considering that the anisotropic expansion is a result of a hydrodynamic evolution governed by η/s, a measurement of the second and third harmonics combined with hydrodynamic calculations can constrain the properties of the medium
The measurements of the flow coefficients, the non-linear modes, symmetryplane corre-lations and the non-linear flow mode coefficients are presented. They are compared with hydrodynamic calculations with various settings [25, 57, 81, 82]
Summary
The limited sensitivity of the elliptic flow to η/s and the large uncertainty in the initial state anisotropy inhibit a precise determination of the value of η/s [34, 36,37,38], and its temperature dependence, which was recently shown to be explorable during the second run of LHC [39, 40]. Part of the anisotropic flow can originate from the hadronic phase [41,42,43] It has been shown in [43, 44] that the inclusion of the temperature dependent bulk viscosity ζ/s(T) in hydrodynamic simulation lead to a better description of the average transverse momentum of charged hadrons and on the elliptic flow coefficient. It was observed that the hydrodynamic models with their respective initial conditions Monte-Carlo (MC)-Glauber [54, 55], MC-KLN [33, 56], and IP-Glasma [57]), are unable to reproduce these measurements, which indicates that the model tuning and η/s parameterization require further work
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