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Elliptic Flow and Fluctuations in Heavy Ion collisions

Elliptic Flow and Fluctuations in Heavy Ion collisions. Marcus Bleicher Institut für Theoretische Physik Goethe Universität - Frankfurt Germany. Thanks to the UrQMD group @ Frankfurt. Sascha Vogel (Resonances and di-leptons) Katharina Schmidt (Di-leptons)

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Elliptic Flow and Fluctuations in Heavy Ion collisions

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  1. Elliptic Flow and Fluctuations in Heavy Ion collisions Marcus Bleicher Institut für Theoretische Physik Goethe Universität - Frankfurt Germany Marcus Bleicher, ETD, Montreal 07/2007

  2. Thanks to the UrQMD group@ Frankfurt • Sascha Vogel (Resonances and di-leptons) • Katharina Schmidt (Di-leptons) • Stephane Haussler (Event-by-Event Fluctuations) • Hannah Petersen (Flow) • Daniel Krieg (Recombination) • Qingfeng Li (HBT) • Xianglei Zhu (Charm) Marcus Bleicher, ETD, Montreal 07/2007

  3. Contents • Introduction • v1 and v2 • v2 fluctuations • Summary Marcus Bleicher, ETD, Montreal 07/2007

  4. Motivation At RHIC: look for signals of partonic matter. (large v2, hydro)At critRHIC/SPS:look for the mixed phase and the onset of deconfinement(flow stalls, large fluctuations, ideal hydro breaks down) E. Bratkovskaya, M.B. et al., PRC 2005 Marcus Bleicher, ETD, Montreal 07/2007

  5. The tool: UrQMDv2.2 • Non-equilibrium transport model • Hadrons and resonances • String excitation and fragmentation • Cross sections are parameterized via AQM or calculated by detailed balance • pQCD hard scattering at high energies • Generates full space-time dynamics of hadrons and strings Marcus Bleicher, ETD, Montreal 07/2007

  6. Multiplicities Comparison to data over the whole energy range E. Bratkovskaya, M.B. et al., PRC 2005 Marcus Bleicher, ETD, Montreal 07/2007

  7. Taken from a talk by B. Lungwitz at CPOD 2007 UrQMD data from Lungwitz& Bleicher, arXiv:0707.1788 Droplets: w > 10-100 (Mishustin) Marcus Bleicher, ETD, Montreal 07/2007

  8. Maybe HBT can deliver… • long life times in the mixed phase… 10 fold increase in life time during the mixed phase Rischke, Gyulassy, Nucl.Phys.A608:479-512,1996 ~ Energy density Marcus Bleicher, ETD, Montreal 07/2007

  9. The HBT puzzle? • Model calculations of RO/RS or (RO2-RS2)1/2 are usually larger than the experimental data Duration time (in the absence of flow): No indication of long life time in the data Li, Bleicher, Stoecker, arXiv:0706.2091. JPG in press Marcus Bleicher, ETD, Montreal 07/2007

  10. Flow is important! • Many observables never fullfilled the promise HBT, fluctuations, J/Psi,…  ideally one should be able to study them at all energies • Transverse collective flow is intimately connected to pressure • Flow is sensitive to changes in the equation of state and therefore to phase transitions (H.Stöcker,W.Greiner Phys.Rep. 137 (1986) 277) Marcus Bleicher, ETD, Montreal 07/2007

  11. Introduction - directed flow Fourier expansion of the azimuthal distribution of the emitted particles : Directed flow with  measures the total amount of transverse flow (J.Y. Ollitrault, Phys. Rev. D, 46; A.M. Poskanzer, S.A. Voloshin, Phys. Rev. C, 58) Reaction plane Marcus Bleicher, ETD, Montreal 07/2007

  12. Excitation function 1-fluid hydro prediction for pxdir : softest point in the EoS leads to decreasing flow from D.Rischke, Y.Pürsün et al. (Heavy Ion Physics 1,309,1995) Marcus Bleicher, ETD, Montreal 07/2007

  13. Antiflow around midrapidity Prediction of antiflow if QGP is produced  softening of the EoS leads to flow in the „wrong“ direction (L.Csernai, Phys.Lett. B 458, 1999) (J.Brachmann et al., Phys.Rev. C, 61, 2000) Marcus Bleicher, ETD, Montreal 07/2007

  14. A problem with hydro • Hydro is not a good tool to study the onset of deconfinement • Agreement at top RHIC energies with ‘wrong’ EoS and ‘wrong’ initial c.(see talk by Dumitru)  try transport Heinz, Kolb,STAR Marcus Bleicher, ETD, Montreal 07/2007

  15. v1 of protons @ 40 AGeV Comparison of rapidity spectra between model and data: • Largest flow at high rapidity values • Centrality dependence visible Data from C.Alt et al., Phys. Rev. C 68, 2003 Petersen et al, Phys.Rev.C74:064908,2006 Marcus Bleicher, ETD, Montreal 07/2007

  16. v1 of protons Slope around midrapidity characterizes shape of the rapidity distribution Extracted from normalized rapidity distribution via polynomial fit At low energies: potentials are important At high energies: data developes negative slope  ´wiggle´ QGP-signal? (L.P. Csernai, Phys.Lett. B 458,1999) Petersen et al, Phys.Rev.C74:064908,2006 Marcus Bleicher, ETD, Montreal 07/2007

  17. Time evolution Pressure  Pressure gradients  Elliptic flow Petersen et al, Phys.Rev.C74:064908,2006 Marcus Bleicher, ETD, Montreal 07/2007

  18. Time evolution at RHIC High-pt Y. Lu et al, J.Phys.G32:1121-1130,2006 Low-pt Elliptic flow builds up in the hadronic stage of the collision Marcus Bleicher, ETD, Montreal 07/2007

  19. v2 (y) of pions @ 40/160 AGeV Petersen et al, Phys.Rev.C74:064908,2006 Pb+Pb Marcus Bleicher, ETD, Montreal 07/2007

  20. v2(y) of protons @40 AGeV • Collapse of elliptic flow? (H.Stöcker, Nucl.Phys. A 750, 2005) • Experimental situation unclear • Transport model calculation is compatible with the data Petersen et al, Phys.Rev.C74:064908,2006 Marcus Bleicher, ETD, Montreal 07/2007

  21. Energy dependence • Qualitative description OK • Importance of potentials at low energies • Lack of pressure shows up at lower SPS energies Petersen et al, Phys.Rev.C74:064908,2006 Marcus Bleicher, ETD, Montreal 07/2007

  22. v2 fluctuations • Tilted axis has to be taken into account with proper (participant) definition of eccentricity Broniowski et al Marcus Bleicher, ETD, Montreal 07/2007

  23. Additional fluctuations • One would expect additional dynamical fluctuations, if the system is not a perfect liquid • Degree of perfection is quantified by the Knudsen number Kn S. Vogel et al., nucl-th/0703031 Marcus Bleicher, ETD, Montreal 07/2007

  24. Fluctuation analysis • To strong fluctuations • Cross section increase, decreases fluctuations S. Vogel et al., nucl-th/0703031 Marcus Bleicher, ETD, Montreal 07/2007

  25. Extrapolation to small Knudsen numbers • Experimental data requires tiny mean free path • 1/Kn > 100-1000 S. Vogel et al., nucl-th/0703031 Bhalerao, PLB2005 Marcus Bleicher, ETD, Montreal 07/2007

  26. Only ideal hydro can do it • Calculation by Kodama et al., • Fluctuating initial state from Nexus • Where is viscosity? Marcus Bleicher, ETD, Montreal 07/2007

  27. Summary • Flow is the ideal tool to study the onset of deconfinement (critRHIC!) • However, ideal hydro fails below top RHIC energy • Unfortunately, hadron/string transport fails above SPS energies • At top RHIC energy: Elliptic flow fluctuations indicate very short mean free path • No sign of ANY turbulence or dynamical fluctuations Marcus Bleicher, ETD, Montreal 07/2007

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