Abstract
The correlations between event-by-event fluctuations of anisotropic flow harmonic amplitudes have been measured in Pb-Pb collisions at sNN=2.76 TeV with the ALICE detector at the Large Hadron Collider. The results are reported in terms of multiparticle correlation observables dubbed symmetric cumulants. These observables are robust against biases originating from nonflow effects. The centrality dependence of correlations between the higher order harmonics (the quadrangular v4 and pentagonal v5 flow) and the lower order harmonics (the elliptic v2 and triangular v3 flow) is presented. The transverse momentum dependences of correlations between v3 and v2 and between v4 and v2 are also reported. The results are compared to calculations from viscous hydrodynamics and a multiphase transport (AMPT) model calculations. The comparisons to viscous hydrodynamic models demonstrate that the different order harmonic correlations respond differently to the initial conditions and the temperature dependence of the ratio of shear viscosity to entropy density (η/s). A small average value of η/s is favored independent of the specific choice of initial conditions in the models. The calculations with the AMPT initial conditions yield results closest to the measurements. Correlations among the magnitudes of v2, v3, and v4 show moderate pT dependence in midcentral collisions. This might be an indication of possible viscous corrections to the equilibrium distribution at hadronic freeze-out, which might help to understand the possible contribution of bulk viscosity in the hadronic phase of the system. Together with existing measurements of individual flow harmonics, the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.6 MoreReceived 1 October 2017DOI:https://doi.org/10.1103/PhysRevC.97.024906Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.©2018 CERN, for the ALICE CollaborationPhysics Subject Headings (PhySH)Research AreasCollective flowNuclear reactionsParticle correlations & fluctuationsRelativistic heavy-ion collisionsNuclear Physics
Highlights
The main emphasis of the ultrarelativistic heavy-ion collision programs at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) is to study the deconfined phase of strongly interacting quantum chromodynamics (QCD) matter, the quark-gluon plasma (QGP)
The symmetric cumulants (SC)(5,2) magnitude is larger than SC(5,3), but the normalized correlation between v5 and v3 is stronger than the normalized correlation between v5 and v2
These results indicate that the lower order harmonic correlations are larger than higher order harmonic correlations, because of the correlation strength itself and because of the strength of the individual flow harmonics
Summary
The main emphasis of the ultrarelativistic heavy-ion collision programs at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) is to study the deconfined phase of strongly interacting QCD matter, the quark-gluon plasma (QGP). The measurements are well described by calculations utilizing viscous hydrodynamics [19,20,21,22,23,24] These calculations demonstrated that the shear viscosity to the entropy density ratio (η/s) of the QGP in heavy-ion collisions at RHIC and LHC energies is close to a universal lower bound 1/4π [25]. The anisotropic flow in heavy-ion collisions is typically understood as the hydrodynamic response of the produced matter to spatial deformations of the initial energy density profile [32]. This profile fluctuates event by event due to fluctuating positions of the constituents inside the colliding nuclei, which implies that vn fluctuates [33,34].
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