Pre-equilibrium dynamics and heavy-ion observables

Abstract

To bracket the importance of the pre-equilibrium stage on relativistic heavy-ion collision observables, we compare simulations where it is modeled by either free-streaming partons or fluid dynamics. These cases implement the assumptions of extremely weak vs. extremely strong coupling in the initial collision stage. Accounting for flow generated in the pre-equilibrium stage, we study the sensitivity of radial, elliptic and triangular flow on the switching time when the hydrodynamic description becomes valid. Using the hybrid code iEBE-VISHNU we perform a multi-parameter search, constrained by particle ratios, integrated elliptic and triangular charged hadron flow, the mean transverse momenta of pions, kaons and protons, and the second moment $⟨p_T^2⟩$ of the proton transverse momentum spectrum, to identify optimized values for the switching time ${\tau }_s$ from pre-equilibrium to hydrodynamics, the specific shear viscosity $\eta /s$, the normalization factor of the temperature-dependent specific bulk viscosity $(\zeta /s)(T)$, and the switching temperature $T_{\mathrm{sw}}$ from viscous hydrodynamics to the hadron cascade UrQMD. With the optimized parameters, we predict and compare with experiment the $p_T$-distributions of $\pi$, $K$, $p$, $\Lambda$, $\Xi$ and $\Omega$ yields and their elliptic flow coefficients, focusing specifically on the mass-ordering of the elliptic flow for protons and Lambda hyperons which is incorrectly described by VISHNU without pre-equilibrium flow.

4 pages, 1 figure. Talk presented at Quark Matter 2015, Kobe, Sep. 27 - Oct. 3, 2015, to appear in the proceedings published by Nuclear Physics A. v2 corrects originally mislabeled curves in Figs. 2a,b

References in corpus (4)

• The equation of state in (2+1)-flavor QCD
• Free-streaming approximation in early dynamics of relativistic heavy-ion collisions
• Collective flow without hydrodynamics: simulation results for relativistic ion collisions
• A hybrid model approach for strange and multi-strange hadrons in 2.76 A TeV Pb+Pb collisions

Cited by in corpus (15)

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• Estimating initial state and quark-gluon plasma medium properties using a hybrid model with nucleon substructure calibrated to $p$-Pb and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV
• Loosely-bound objects produced in nuclear collisions at the LHC
• Collective flow in 2.76 A TeV and 5.02 A TeV Pb+Pb collisions
• Bayesian estimation of the specific shear and bulk viscosity of the quark-gluon plasma with additional flow harmonic observables
• Massively parallel simulations of relativistic fluid dynamics on graphics processing units with CUDA
• Bayesian parameter estimation for relativistic heavy-ion collisions
• Revisit the Chiral Magnetic Effect Expectation in Isobaric Collisions at the Relativistic Heavy Ion Collider
• A data-driven analysis of the heavy quark transport coefficient
• Initial conditions of bulk matter in ultrarelativistic nuclear collisions
• Influence of the chiral magnetic effect on particle-pair elliptic anisotropy
• Hydrodynamic Overview at Hot Quarks 2016