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Elliptic Flow Results From a Hybrid Model

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1 Elliptic Flow Results From a Hybrid Model
Workshop on „Flow and Dissipation in Ultrarelativistic Heavy Ion Collisions" , Trento, Italy Hannah Petersen, Universität Frankfurt Thanks to: Jan Steinheimer, Marcus Bleicher Dirk Rischke (for providing the hydrodynamics code)

2 Outline Model Description Elliptic Flow Conclusions and Outlook
Initial Conditions Equations of State (EoS) Freeze-out Scenarios Elliptic Flow Comparison of Initial States Time Evolution Dependence on the EoS Influence of the Transition Criterion Conclusions and Outlook (H.P. et al., PRC 78:044901, 2008, arXiv: ) Hannah Petersen Trento,

3 Hybrid Approaches Hadronic freezeout following a first order hadronization phase transition in ultrarelativistic heavy ion collisions. S.A. Bass, A. Dumitru, M. Bleicher, L. Bravina, E. Zabrodin, H. Stoecker, W. Greiner, Phys.Rev.C60:021902,1999 Dynamics of hot bulk QCD matter: From the quark gluon plasma to hadronic freezeout. S.A. Bass, A. Dumitru, Phys.Rev.C61:064909,2000 Flow at the SPS and RHIC as a quark gluon plasma signature. D. Teaney, J. Lauret, Edward V. Shuryak, Phys.Rev.Lett.86: ,2001 A Hydrodynamic description of heavy ion collisions at the SPS and RHIC. D. Teaney, J. Lauret, E.V. Shuryak, e-Print: nucl-th/ Hadronic dissipative effects on elliptic flow in ultrarelativistic heavy-ion collisions. T. Hirano, U. Heinz, D. Kharzeev, R. Lacey, Y. Nara, Phys.Lett.B636: ,2006 3-D hydro + cascade model at RHIC. C. Nonaka, S.A. Bass, Nucl.Phys.A774: ,2006 Results On Transverse Mass Spectra Obtained With Nexspherio F. Grassi, T. Kodama, Y. Hama, J.Phys.G31:S1041-S1044,2005 On the Role of Initial Conditions and Final State Interactions in Ultrarelativistic Heavy Ion Collisions K. Werner, T. Hirano, I. Karpenko, T. Pierog, S. Porteboeuf, M. Bleicher, S. Haussler J.Phys.G36:064030, 2009 Hannah Petersen Trento,

4 Motivation Exploring the differences between transport and hydrodynamics within the same initial conditions and freeze-out Calculation with different EoS without adjusting anything else Investigate effects of ingredients in a systematic way Many observables within the same dynamical approach  Here: Concentrate on elliptic flow Hannah Petersen Trento,

5 Principle Set-Up Fix the initial state and freeze-out
 learn something about the EoS and the effect of viscous dynamics 2) Hydrodynamic evolution or Transport calculation 3) Freeze-out via hadronic cascade (UrQMD) 1) Non-equilibrium initial conditions via UrQMD UrQMD-2.3p1 is available at Hannah Petersen Trento,

6 Initial State Contracted nuclei have passed through each other
Energy is deposited Baryon currents have separated Energy-, momentum- and baryon number densities are mapped onto the hydro grid Event-by-event fluctuations are taken into account Spectators are propagated separately in the cascade (nucl-th/ , nucl-th/ ) Elab=40 AGeV b=0 fm (J.Steinheimer et al., PRC 77,034901,2008) Hannah Petersen Trento,

7 (3+1)d Hydrodynamic Evolution
Ideal relativistic one fluid dynamics employing: HG: Hadron gas including the same degrees of freedom as in UrQMD (all hadrons with masses up to 2.2 GeV) CH: Chiral EoS from SU(3) hadronic Lagrangian with first order transition and critical endpoint BM: Bag Model EoS with a strong first order phase transition between QGP and hadronic phase D. Rischke et al., NPA 595, 346, 1995, D. Rischke et al., NPA 595, 383, 1995 Papazoglou et al., PRC 59, 411, 1999 Hannah Petersen Trento,

8 Freeze-out Transition from hydro to transport when e < 730 MeV/fm³ (≈ 5 * e0) in all cells of one transverse slice (Gradual freeze-out, GF)  iso-eigentime criterion Transition when e < 5* e0 in all cells (Isochronuous freeze-out, IF) Chemical FO by Cleymans et al. Particle distributions are generated according to the Cooper-Frye formula with boosted Fermi or Bose distributions f(x,p) including mB and mS Rescatterings and final decays calculated via hadronic cascade (UrQMD) Hannah Petersen Trento,

9 Final State Interactions
Hannah Petersen Trento,

10 Time Evolution Central Pb+Pb collisions at 40A GeV:
Number of particles decreases in the beginning due to resonance creation Qualitative behaviour very similar in both calculations  UrQMD equilibrates to a rather large degree Hannah Petersen Trento,

11 Multiplicities vs. Energy
full lines: hybrid model (IF) squares: hybrid model (GF) dotted lines: UrQMD-2.3 symbols: experimental data Both models are purely hadronic without phase transition, but different underlying dynamics  Results for particle multiplicities from AGS to SPS are similar  Strangeness is enhanced in the hybrid approach due to local equilibration L X W (H.P. et al., PRC 78:044901, 2008) p K P Central (b<3.4 fm) Pb+Pb/Au+Au collisions Data from E895, NA49 Hannah Petersen Trento,

12 Strangeness Centrality Dependence
Thermal production of the particles at transition from hydro to transport Centrality dependence of multistrange hyperons is improved hybrid model (GF) ----- UrQMD-2.3 (H.P. et al., arXiv: ) Pb+Pb collisions for different centralities Hannah Petersen Trento,

13 Initial State for Non-Central Collisions
Pb+Pb at Elab=40 AGeV with b= 7fm at tstart=2.83 fm Energy density profile Weighted velocity profile GeV/fm3 GeV/fm3 Event-by-event fluctuations are taken into account (H.P. et.al., PRC 79, , 2009) Hannah Petersen Trento,

14 Comparison of Initial Conditions
Elab=160A GeV, mid-central Averaged (over 100 events) Fluctuating (default) Glauber (Npart) UrQMD initial conditions have a different shape than the ones from a Glauber model (parameters taken from Teaney et al. nucl-th/ ) Hannah Petersen Trento,

15 Initial Transverse Velocity Profile
The initial velocity is finite in transverse direction <bT>=0.09 <bT>=0.05  Test influence by setting vx and vy to zero Mid-central (b=5-9 fm) Pb+Pb collisions Hannah Petersen Trento,

16 Rapidity Spectra  Rapidity spectra for pions and kaons are steeper for averaged initial conditions and independent of the initial transverse velocity profiles Central (b<3.4 fm) Pb+Pb/Au+Au collisions Hannah Petersen Trento,

17 Transverse Mass Spectra
Blue: pions Green: protons Red: kaons 40A GeV 160A GeV The transverse mass distributions for pions, kaons and protons do not dependent on the initial conditions Difference in the dynamics between hydro and transport becomes visible at 160A GeV Central (b<3.4 fm) Pb+Pb collisions Hannah Petersen Trento,

18 Elliptic Flow-Initial Conditions
v2 is largely insensitive to the initial conditions from UrQMD with respect to fluctuations and inital velocity profile Hannah Petersen Trento,

19 Flow from Different Stages
v2 is mostly generated during the hydrodynamic expansion Afterburner effect might be larger with different transition criterion Hannah Petersen Trento,

20 Time Evolution of Elliptic Flow
Elliptic flow develops after tstart in the hadronic transport approach Different EoS lead to very different behaviour Hannah Petersen Trento,

21 v2 Excitation Function for Different EoS
Final observable value does not depend on EoS  Influence of transition criterion Hannah Petersen Trento,

22 Transverse Momentum Dependence
Protons Pions NA49 (NA49, PRC 68, , 2003) Hydro phase leads to higher flow values, but weak EoS dependence Hannah Petersen Trento,

23 Dependence on Transition Criterion
Smaller mean free path in the hot and dense phase leads to higher elliptic flow At lower energies: hybrid approach reproduces the pure UrQMD result Gradual transition leads to a better description of the data (H.P. et.al., PRC 79, , 2009) Data from E895, E877, NA49, Ceres, Phenix, Phobos, Star Hannah Petersen Trento,

24 Conclusions and Outlook
Integrated approach with the same initial conditions and freeze-out for different EoS v2 is largely insensitive to the initial conditions from UrQMD with respect to fluctuations and inital velocity profile Averaged UrQMD initial conditions are still different than those from a Glauber model Final observable flow is rather insensitive to the EoS Elliptic flow is sensitive to the dynamics (transport vs hydro with the same initial conditions) and therefore to viscosity Choice of transition criterion results in a systematic uncertainity on the order of 20 % Compare calculations with different initial conditions like e.g. Glauber, CGC, Gaussian ... Implement different transition hypersurfaces (iso-T, iso-r,..) Hannah Petersen Trento,

25 Backup

26 RO/RS Ratio Hydro phase leads to smaller ratios
Hydro to transport transition does not matter, if final rescattering is taken into account EoS dependence is visible, but not as strong as previuosly predicted (factor of 5) Data from NA49 (Q. Li et al., PLB 674, 111, 2009) Hannah Petersen Trento,

27 HBT radii (Q. Li et al., arXiv: , PLB in print) Hydro evolution leads to larger radii, esp. with phase transition Hannah Petersen Trento,

28 Freeze-out line Parametrization of chemical freeze-out line taken from
Cleymans et al, J.Phys. G 32, S165, 2006 Green points are from A.Dumitru et al., PRC 73, , 2006  Mean values and widths are in line with other calculations 5*e0 Black: Gradual FO Red: Isochronuous FO Hannah Petersen Trento,

29 Temperature Distributions
Rapidity distribution of the freeze-out temperatures in central Au+Au/Pb+Pb collisions with hadron gas EoS Isochronuous freeze-out Gradual freeze-out Hannah Petersen Trento,

30 v2/e Scaling More realistic initial conditions and freeze-out
Qualitative behaviour nicely reproduced Uncertainty due to eccentricity calculation Avaraged over particles and events at the same time Averaged first over particles and then over events Hannah Petersen Trento,

31 Dependence on Freeze-out
Variation of the freeze-out criterium does not affect the meson multiplicities and mean transerve masses Full symbols: 40 AGeV Open symbols: 11 AGeV Hannah Petersen Trento,

32 Dependence on tstart Variation of starting time by a factor 4 changes results only by 10 % Full symbols: 40 AGeV Open symbols: 11 AGeV Hannah Petersen Trento,

33 Time scales Hannah Petersen Trento,

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