Viscosity, non-conformal equation of state and sound velocity in Landau hydrodynamics

Abstract

We find an analytical solution to relativistic viscous hydrodynamics for a 1+1 dimensional Landau flow profile. We consider relativistic Navier-Stokes form of the dissipative hydrodynamic equation, for a non-conformal system with a constant speed of sound, and employ the obtained solution to fit rapidity spectrum of observed pions in $\sqrt{s_{NN}}=$ 200, 17.3, 12.3, 8.76, 7.62, 6.27, 4.29, 3.83, 3.28 and 2.63 GeV collision energies. We find that at the freeze-out hypersurface with improved Landau's freeze-out prescription, the viscous corrections do not affect the rapidity spectra. We demonstrate that the solution of the non-conformal Landau flow lead to a better agreement with the experimental data compared to the conformal ideal solution. We also extract speed of sound from fit to the rapidity spectra for various collision energies and find a monotonous decrease with decreasing collision energies. Appealing to the fact that viscosity has negligible effect on rapidity spectra for Landau's freeze-out scenario, we argue that our calculations provides a framework for extracting the average value of speed of sound in relativistic heavy-ion collisions.

7 pages, 2 figures, published version

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• Formation of light nuclei at chemical freezeout: Description within a statistical thermal model
• Hierarchy of kinetic freeze-out parameters in low energy heavy-ion collisions
• Hadron momentum spectra from analytical solutions of relativistic hydrodynamics
• On the Square Speed of Sound in High-Energy Collisions: Range of Values and How to Understand It