Article

# Influence of a temperature-dependent shear viscosity on the azimuthal asymmetries of transverse momentum spectra in ultrarelativistic heavy-ion collisions

(Impact Factor: 3.73). 03/2012; 86(1). DOI: 10.1103/PhysRevC.86.014909
Source: arXiv

ABSTRACT

We study the influence of a temperature-dependent shear viscosity over
entropy density ratio $\eta/s$, different shear relaxation times $\tau_\pi$, as
well as different initial conditions on the transverse momentum spectra of
charged hadrons and identified particles. We investigate the azimuthal flow
asymmetries as a function of both collision energy and centrality. The elliptic
flow coefficient turns out to be dominated by the hadronic viscosity at RHIC
energies. Only at higher collision energies the impact of the viscosity in the
QGP phase is visible in the flow asymmetries. Nevertheless, the shear viscosity
near the QCD transition region has the largest impact on the collective flow of
the system. We also find that the centrality dependence of the elliptic flow is
sensitive to the temperature dependence of $\eta/s$.

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Available from: Gabriel S. Denicol, Mar 13, 2014
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• "Since the early days of ideal hydrodynamics there has been a concerted effort to make hydrodynamical models more realistic by including the effect of shear and bulk viscosities (relaxation times). This has lead to a proper formulation of relativistic viscous hydrodynamics [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] and, recently, anisotropic relativistic viscous hydrodynamics [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29]. The conclusion one reaches from dissipative hydrodynamics approaches is that the QGP created in ultrarelativistic heavy ion collisions (URHICs) has quite different longitudinal (along the beam line) and transverse pressures, particularly at times τ ∼ < 2 fm/c. "
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Nuclear Physics A 01/2014; 926. DOI:10.1016/j.nuclphysa.2014.01.013 · 2.20 Impact Factor
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• "The inclusion of dissipative effects in the description of the QGP started only a few years ago. To date the majority of studies have focused on investigating the effects of the shear viscosity in the time evolution of the QGP and in extracting its magnitude from HIC measurements [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]. Nevertheless, there are other sources of dissipation that might play a role in the fluid-dynamical description of HIC, such as bulk viscous pressure and heat flow. "
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ABSTRACT: We investigate the entropy production within dissipative hydrodynamics in the Israel-Stewart (IS) and Navier-Stokes theory (NS) for relativistic heavy ion physics applications. In particular we focus on the initial condition in a 0+1D Bjorken scenario, appropriate for the early longitudinal expansion stage of the collision. Going beyond the standard simplification of a massless ideal gas we consider a realistic equation of state consistently derived within a virial expansion. The EoS used is well in line with recent three-flavor QCD lattice data for the pressure, speed of sound, and interaction measure at nonzero temperature and vanishing chemical potential ($\mu_{\rm q} = 0$). The shear viscosity has been consistently calculated within this formalism using a kinetic approach in the ultra-relativistic regime with an explicit and systematic evaluation of the transport cross section as function of temperature. We investigate the influence of the viscosity and the initial condition, i.e. formation time, initial temperature, and pressure anisotropy for the entropy production at RHIC at $\sqrt{s_{\rm NN}}=130$ GeV. We find that the interplay between effects of the viscosity and of the realistic EoS can not be neglected in the reconstruction of the initial state from experimental data. Therefore, from the experimental findings it is very hard to derive unambiguous information about the initial conditions and/or the evolution of the system.
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