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تسجيل مستخدم جديدEffects of EoS in viscous hydro+cascade model for the RHIC Beam Energy Scan
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A state-of-the-art 3+1 dimensional cascade + viscous hydro + cascade model vHLLE+UrQMD has been applied to heavy ion collisions in RHIC Beam Energy Scan range $sqrt{s_{rm NN}}=7.7dots 200$ GeV. Based on comparison to available experimental data it was estimated that an effective value of shear viscosity over entropy density ratio $eta/s$ in hydrodynamic stage has to decrease from $eta/s=0.2$ to $0.08$ as collision energy increases from $sqrt{s_{rm NN}} = 7.7$ to $39$ GeV, and to stay at $eta/s=0.08$ for $39lesqrt{s_{rm NN}}le200$ GeV. In this work we show how an equation of state with first order phase transition affects the hydrodynamic evolution at those collision energies and changes the results of the model as compared to default scenario with a crossover type EoS from chiral model.
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Following the experimental program at BNL RHIC, we perform a similar energy scan using 3+1D viscous hydrodynamics coupled to the UrQMD hadron cascade, and study the collision energy dependence of pion and kaon rapidity distributions and $m_T$-spectra
, as well as charged hadron elliptic flow. To this aim the equation of state for finite baryon density from a Chiral model coupled to the Polyakov loop is employed for hydrodynamic stage. 3D initial conditions from UrQMD are used to study gradual deviation from boost-invariant scaling flow. We find that the inclusion of shear viscosity in the hydrodynamic stage of evolution consistently improves the description of the data for Pb-Pb collisions at CERN SPS, as well as of the elliptic flow measurements for Au-Au collisions in the Beam Energy Scan (BES) program at BNL RHIC. The suggested value of shear viscosity is $eta/sge0.2$ for $sqrt{s_{NN}}=6.3dots39$ GeV.
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