Auvinen, J.

Elfner, Hannah

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Collision Energy Evolution of Elliptic and Triangular Flow in a Hybrid Model∗J. Auvinen1 and H. Petersen1,21Frankfurt Institute for Advanced Studies, Frankfurt am Main, Germany; 2Institut fu¨r Theoretische Physik, GoetheUniversita¨t Frankfurt, Frankfurt am Main, GermanyWe have studied the collision energy dependence of el-liptic flow v2 and triangular flow v3 in Au+Au collisionswithin the energy range √sNN = 5 − 200 GeV, utiliz-ing a transport + hydrodynamics hybrid model [1,2]. Thetransport part is described by the Ultrarelativistic Quan-tum Molecular Dynamics (UrQMD), combined with an in-termediate (3+1)-dimensional ideal hydrodynamical evo-lution phase using a chiral model equation of state. Thisapproach provides a consistent framework for investigat-ing both high-energy heavy ion collisions with negligiblenet-baryon density and a large hydrodynamically evolvingmedium, and the collisions at smaller energies with finitenet-baryon density, where the hydrodynamics phase is veryshort-lived or does not exist at all.The hybrid model reproduces the qualitative behavior ofthe experimentally measured elliptic flow (see Fig. 1(a)).While v2 produced by hydrodynamics is considerably di-minished at lower collision energies, this decrease is par-tially compensated by the transport dynamics, as shown inFig. 1(b). The pre-hydrodynamics transport phase is of par-ticular importance for understanding the collision energyevolution, while the hadronic rescatterings after the hydro-dynamical phase contribute more systematically ∼ 10% tothe total flow at all energies. However, the viscous matterdescribed by transport dynamics is unable to produce trian-gular flow, which consequently shows a significantly largerrelative decrease in midcentral collisions with decreasing√sNN (Fig. 1(c)). Our conclusion is that the triangularflow provides the clearer signal for the formation of low-viscous fluid in heavy ion collisions.References[1] J. Auvinen and H. Petersen, ”Collision Energy Evolution ofElliptic and Triangular Flow in a Hybrid Model”, PoS CPOD2013 (2013) 034[2] J. Auvinen and H. Petersen, ”Evolution of elliptic and tri-angular flow as a function of collision energy in a hybridmodel”, Phys. Rev. C 88 (2013) 064908[3] L. Adamczyk et al. [STAR Collaboration], “Inclusivecharged hadron elliptic flow in Au + Au collisions at √sNN= 7.7 - 39 GeV”, Phys. Rev. C 86 (2012) 054908[4] J. Adams et al. [STAR Collaboration], “Azimuthal anisotropyin Au+Au collisions at √sNN = 200-GeV”, Phys. Rev. C 72(2012) 014904∗Work supported by HIC for FAIR and Helmholtz-NachwuchsgruppeVH-NG-822. Computational resources have been provided by the Centerfor Scientific Computing (CSC) at Goethe Universita¨t Frankfurt.Integrated v200.010.020.030.040.050.060.070.080.090.1√sNN [GeV]10 100STAR v2{EP} ( 0 - 5 )% Hybrid v2{EP} b = 0 - 3.4 fmSTAR v2{EP} (20 - 30)% Hybrid v2{EP} b = 6.7 - 8.2 fmSTAR v2{EP} (30 - 40)% Hybrid v2{EP} b = 8.2 - 9.4 fm           Charged hadrons                        |η| < 1.00.2 GeV < pT < 2.0 GeVa)Charged hadrons, b = 8.2 - 9.4 fmIntegrated v200.010.020.030.040.050.060.070.08√sNN [GeV]10 100Before hydroAfter hydroAfter hadronic rescatteringEvent plane analysisb)Integrated v3−0.00500.0050.010.0150.020.025√sNN [GeV]10 100Hybrid v3{EP} b = 0 - 3.4 fmHybrid v3{EP} b = 6.7 - 8.2 fm           Charged hadrons                        |η| < 1.00.2 GeV < pT < 2.0 GeVc)Figure 1: a): Integrated elliptic flow v2{EP} for charged hadronswith 0.2 < pT < 2.0 at midrapidity |η| < 1.0 in Au+Au -collisions, for collision energies √sNN = 7.7 − 200 GeV andthree different impact parameter ranges, compared with the STARdata [3, 4]. b): Magnitude of v2{EP} in midcentral collisions(b = 8.2− 9.4 fm) at the beginning of hydrodynamical evolution(diamonds), immediately after the end of hydrodynamics phase(squares) and after the full simulation (circles). c): Integratedv3{EP} in central collisions (b = 0− 3.4 fm, open triangles) andmidcentral collisions (b = 6.7− 8.2 fm, solid triangles).THEORY-16 GSI SCIENTIFIC REPORT 2013268 doi:10.15120/GR-2014-1-THEORY-16

Collision Energy Evolution of Elliptic and Triangular Flow in a Hybrid Model

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Collision Energy Evolution of Elliptic and Triangular Flow in a Hybrid Model

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