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Longitudinal Flow and Onset of Deconfinement

Longitudinal Flow and Onset of Deconfinement. Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany. Outline of the talk. Introduction Fluctuations  Evidence for mixing Rapidity widths + Landau  softest point Summary. The tool: UrQMD v2.2.

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Longitudinal Flow and Onset of Deconfinement

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  1. Longitudinal Flow and Onset of Deconfinement Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany Marcus Bleicher, Florence 2006

  2. Outline of the talk • Introduction • Fluctuations  Evidence for mixing • Rapidity widths + Landau  softest point • Summary Marcus Bleicher, Florence 2006

  3. 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, Florence 2006

  4. Thanks to the UrQMD group@ Frankfurt • Sascha Vogel (Resonances) • Stephane Haussler (Event-by-Event Fluctuations) • Hannah Petersen (Flow at FAIR) • Diana Schumacher (Di-Leptons) • Qingfeng Li (Isospin Dynamics & HBT) • Xianglei Zhu (Elliptic Flow and Charm) • Mohamed Abdel-Aziz (Event-by-Event Fluctuations) • Elena Bratkovskaya (HSD) • and Horst Stoecker (keeping it running) Marcus Bleicher, Florence 2006

  5. Motivation At RHIC: look for signals of freely moving partons.At FAIR/SPS:look for the mixed phase and the onset of deconfinement E. Bratkovskaya, M.Bleicher. et al., PRC 2005 Marcus Bleicher, Florence 2006

  6. Excitation functions: ratios • ‘Horn’ in the ratio not reproduced • well reproduced • relative strange baryon enhancement reproduced E. Bratkovskaya, M.Bleicher. et al., PRC 2005 Marcus Bleicher, Florence 2006

  7. Fluctuation studies • K/p fluctuations increase towards lower beam energy • Significant enhancement over hadronic cascade model • p/p fluctuations are negative • indicates a strong contribution from resonance decays Taken from Christoph Roland NA49 Preliminary NA49 Preliminary Marcus Bleicher, Florence 2006

  8. Energy dependence • Qualitative description OK • Importance of potentials at low energies • Lack of pressure shows up at SPS energies • EoS <-> Flow H. Petersen, X. Zhu, M.B. Marcus Bleicher, Florence 2006

  9. ‘Partonic’ dof already atlow SPS energy • Breakdown of v2 in model coincides with onset of ‘partonic’ matter signals onset of change of EoS in the early stage 30 AGeV H. Petersen, X. Zhu, M.B. Marcus Bleicher, Florence 2006

  10. Stopping power UrQMD vs data Pb+Pb/Au+Au • Linear increase of rapidity shift at low energies • ‘Saturation’ above highest SPS energy • However, relative momentum loss is energy independent Marcus Bleicher, Florence 2006

  11. Multiplicities • Temperatures • Elliptic Flow • Correlations have already been studied Can we learn more from the longitudinal dynamics? Marcus Bleicher, Florence 2006

  12. Multiplicity fluctuations Pb+Pb (158 AGeV) in the NA49 acceptance (1.1<yCM<2.9) Extraction of the multiplicity distribution for every NparNote: Calculation is narrower than the data for Npar~45 Marcus Bleicher, Florence 2006

  13. Multiplicity fluctuations at SPS:The problem • The fluctuation is quantified with the • scaled variance : • Enhanced fluctuations for mid- • peripheral collisions are observed Similar results from HIJING, HSD and RQMD Note : - for a poisson distribution, w=1 Marcus Bleicher, Florence 2006

  14. Where is the problem? Pb+Pb (158 AGeV) in the NA49 acceptance (1.1<yCM<2.9) • Mean value correctly reproduced • Variance reproduced for central and very peripheral events • Failure for mid-peripheral events Marcus Bleicher, Florence 2006

  15. Analysis of different windows • the normalized variance : • flat in the projectile hemisphere • larger in the mirror acceptance • even larger in 4p • maximum around Np=40 Konchakovski, Haussler,…, PRC 73 (2006) Marcus Bleicher, Florence 2006

  16. Fluctutions in target region • the fluctuation has a maximum • around Np=25 • introduces an asymetry between • projectile and target participants • leads to an increase of the multiplicity • fluctuation in the target hemisphere Marcus Bleicher, Florence 2006

  17. Correlation length in rapidity • Rapidity window dependence : • correlation length of the order of 1 • unit of rapidity • target and projectile hemisphere are • independent in hadron-string models Marcus Bleicher, Florence 2006

  18. Mixing and fluctuations • I.e. the trigger condition ‘marks’ projectile and target participants • This allows to study the degree of mixing of the matter produced in HIC • Data suggest strong mixing of hemispheres • Hints to expanding initial fireball in contrast to string dynamics M. Gazdzicki and M. Gorenstein:arXiv:hep-ph/0511058 Marcus Bleicher, Florence 2006

  19. What the fluctuations told us… • Initial fireball of newly produced particles • Fireball seems to expand Landau-like • Leads to strong correlations in rapidity We might use Landau-type hydro to explore the properties of this matter Marcus Bleicher, Florence 2006

  20. Pion rapidity density • Pions rapidity densities are Gaussians at all energies D. Ouerdane, QM04 Marcus Bleicher, Florence 2006

  21. Different particle types • NA49 data yields Gaussian rapidity distributions • Also ALL other experiments report Gaussians for newly produced particles Marcus Bleicher, Florence 2006

  22. Fireball expansion • Assumptions:- applies only to newly produced particles- Lorentz contracted nuclei- simplified Hagedorn gas EoS E. Shuryak, Yad. Fiz. 16 (1972) 395similar to Landau hydroFor more praise on Landau hydro see. P. Steinberg Marcus Bleicher, Florence 2006

  23. Rapidity widths • Rapidity width scales linearly with projectile rapidity M. Bleicher, hep-ph/0509314 Marcus Bleicher, Florence 2006

  24. Speed of sound • Analysis of the rapidity data indicates a softest point at20-30 AGeV beam energy M. Bleicher, hep-ph/0509314 Marcus Bleicher, Florence 2006

  25. Its soft, but… • …is it the mixed phase? • UrQMD also describes the rapidity widths • UrQMD has a soft equation of state Marcus Bleicher, Florence 2006

  26. Summary • Fluctuations indicate strongly mixed initial stage • Assumption of Landau-type hydro allows to extract speed of sound from rapidity widths • Apparent local minimum of sound velocity around 20 – 30 AGeV • Nature of this softest point is unclear Marcus Bleicher, Florence 2006

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