Linear and cubic response to the initial eccentricity in heavy-ion collisions

Abstract

We study the relation between elliptic flow, v2 and the initial eccentricity, ε2, in heavy-ion collisions, using hydrodynamic simulations. Significant deviations from linear eccentricity scaling are seen in more peripheral collisions. We identify the mechanism responsible for these deviations as a cubic response, which we argue is a generic property of the hydrodynamic response to the initial density profile. The cubic response increases elliptic flow fluctuations, thereby improving agreement of initial condition models with experimental data.

Energy dependence and fluctuations of anisotropic flow in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ and 2.76 TeV

“…In particular, k 2 is expected to be ≤ 0.15 in the centrality range 0-60% [81]. The residual differences in α, ε 0 and k 2 when including k 2 as an additional free parameter are considered in the systematic uncertainties.…”

“…This coefficient is introduced to quantify the possible increase of flow fluctuations that the hydrodynamic expansion of the medium introduces with respect to geometrical fluctuations in the initial state and was argued to be non-zero in mid-central and peripheral collisions due to general properties of the hydrodynamic phase [81]. In particular, k 2 is expected to be ≤ 0.15 in the centrality range 0-60% [81].…”

Mode-coupling effects in anisotropic flow in heavy-ion collisions

“…Theoretical calculations have shown that for elliptic and triangular flows (n = 2, 3), the magnitudes of the anisotropic flow coefficients v n are approximately linear in the magnitude of the initial eccentricity coefficients arXiv:1602.02813v2 [nucl-th] 30 Mar 2016 n , except for large impact parameters [5][6][7][8][9]. Since shear viscosity reduces the hydrodynamic response v n to the initial eccentricity n , v n / n for n = 2, 3 was proposed in [5,10] as a clean observable to quantitatively constrain the shear viscosity of quark-gluon plasma.…”

Event-by-EventHydrodynamics+JetEnergy Loss: A Solution to theRAA⊗vNoronha-Hostler1, Betz2, Noronha3 et al. 2016Phys. Rev. Lett.Self Cite11861573View full textAdd to dashboardCite

“…It is now understood [54] that the initial spatial anisotropies present in the early stages of nucleus-nucleus collisions are converted to final stage momentum anisotropies (i.e., anisotropic flow) in a way that is consistent with viscous relativistic hydrodynamic simulations performed on an event-by-event basis (see, e.g., the review [47]). Furthermore, once the full information regarding the soft event-by-event v n distributions became available [55] at the LHC, powerful constraints on the initial conditions of the hydrodynamic modeling of the QGP have been obtained [56][57][58][59][60]. Nevertheless, these recent advances regarding event-by-event medium fluctuations have not yet been incorporated in theoretical studies of high p T observables.…”