Hydrodynamic fluctuations and ultra-central flow puzzle in heavy-ion collisions

Abstract

One of the long-standing problems in the field of high-energy heavy-ion collisions is that the dynamical models based on viscous hydrodynamics fail to describe the experimental elliptic flow $v_2$ and the triangular flow $v_3$ simultaneously in ultra-central collisions. The problem, known as the "ultra-central flow puzzle", is specifically that hydrodynamics-based models predict the flow ratio of the two-particle cumulant method $v_2\{2\}/v_3\{2\}>1$ while $v_2\{2\}/v_3\{2\}\sim 1$ in the experimental data. In this Letter, we focus on the effects of hydrodynamic fluctuations during the space-time evolution of the QGP fluid on the flow observables in the ultra-central collisions. Using the (3+1)-dimensional integrated dynamical model which includes relativistic fluctuating hydrodynamics, we analyze the anisotropic flow coefficients $v_n\{2\}$ in 0-0.2% central Pb+Pb collisions at $\sqrt{s_{\text{NN}}}=2.76\text{TeV}$. We find that the hydrodynamic fluctuations decrease the model overestimate of $v_2\{2\}/v_3\{2\}$ from the experimental data by about 19% within the present setup of $\eta /s=1/2\pi$. This means that the hydrodynamic fluctuations qualitatively have an effect to improve the situation for the puzzle, but the effect of the hydrodynamic fluctuations alone is quantitatively insufficient to resolve the puzzle. The decrease of the ratio largely depends on the shear viscosity $\eta /s$, which calls for future comprehensive analyses with, for example, a realistic temperature-dependent viscosity.

7 pages, 5 figures

References in corpus (17)

• Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics
• Multi-system Bayesian constraints on the transport coefficients of QCD matter
• Bayesian analysis of heavy ion collisions with the heavy ion computational framework Trajectum
• Anisotropic flow in sqrt(s)=2.76 TeV Pb+Pb collisions at the LHC
• Translation of collision geometry fluctuations into momentum anisotropies in relativistic heavy-ion collisions
• Phenomenological constraints on the transport properties of QCD matter with data-driven model averaging
• Title Quantum Optics and Heavy Ion Physics
• Temperature dependence of $\eta /s$ of strongly interacting matter: effects of the equation of state and the parametric form of $(\eta /s)(T)$
• Shape and flow fluctuations in ultra-central Pb+Pb collisions at the LHC
• Extracting the bulk viscosity of the quark-gluon plasma
• Collective flow in event-by-event partonic transport plus hydrodynamics hybrid approach
• Rapidity decorrelation of anisotropic flow caused by hydrodynamic fluctuations
• Causal Viscous Hydrodynamics for Relativistic Heavy Ion Collisions
• Possible octupole deformation of ${}^{208}$Pb and the ultracentral $v_2$ to $v_3$ puzzle
• Effects of hydrodynamic and initial longitudinal fluctuations on rapidity decorrelation of collective flow
• Gluonic Hot Spot Initial Conditions in Heavy-Ion Collisions
• Collective nuclear vibrations and initial state shape fluctuations in central Pb+Pb collisions: resolving the $v_2$ to $v_3$ puzzle

Cited by in corpus (5)

• Progress and Challenges in Small Systems
• Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations
• Impact parameter dependence of anisotropic flow: Bayesian reconstruction in ultracentral nucleus-nucleus collisions
• System size and shape dependences of collective flow fluctuations in relativistic nuclear collisions
• Causal hydrodynamic fluctuations in a one-dimensional expanding system