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Strangeness Dynamics and Transverse Pressure in HIC

Strangeness Dynamics and Transverse Pressure in HIC. Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany. Contents. Chemical equilibrium stage: The ‘horn’, the ‘step’ Kinetic decoupling stage: Resonance (non-) suppression Summary. The tool: UrQMD.

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Strangeness Dynamics and Transverse Pressure in HIC

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  1. Strangeness Dynamics andTransverse Pressure in HIC Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany Marcus Bleicher, CCAST- Workshop 2004

  2. Contents • Chemical equilibrium stage: The ‘horn’, the ‘step’ • Kinetic decoupling stage: Resonance (non-) suppression • Summary Marcus Bleicher, CCAST- Workshop 2004

  3. The tool: UrQMD • Non-equilibrium transport model • Hadrons and resonances • String excitation and fragmentation • Cross sections are parametrizedvia AQM or calculated by detailed balance • Generates full space-time dynamics of hadrons and strings Marcus Bleicher, CCAST- Workshop 2004

  4. Part I: Evidence for the tri-critical point? • 1st Order phase transition at high • No P.T. at low • Search for irregularities around Ebeam = 10-40 GeV: • Flow, strangeness, E-by-E Marcus Bleicher, CCAST- Workshop 2004

  5. Collision Spectrum • Initial stage scattering before 1.5 fm/c:Baryon stopping, meson production, may be QGP formation • Thermalization stage (1.5 – 6 fm/c):Cooking QCD matter • Hadronic freeze-out stage (6 – 10 fm/c):Elastic and pseudo-elastic hadron scatterings Pb+Pb @ 160 AGeV Marcus Bleicher, CCAST- Workshop 2004

  6. Excitation functions • 4 and midrapidity abundancies: OK • Energy dependence: OK • Hadron-string models work well Marcus Bleicher, CCAST- Workshop 2004

  7. Excitation functions: ratios • ‘Horn’ in the ratio not reproduced • well reproduced • relative strange baryon enhancement reproduced Marcus Bleicher, CCAST- Workshop 2004

  8. Ratio excitation functions: Summary • Yields are well reproduced • Most ratios can be understood in transport models • Model K/pi ratio does not reproduce the strong peak observed in data Marcus Bleicher, CCAST- Workshop 2004

  9. Proton-Proton • PP works well • pQCD needed at RHIC • PYTHIA included in • UrQMD 2.x and HSD Marcus Bleicher, CCAST- Workshop 2004

  10. Proton-Nucleus • pA is well under control • What about AA? Marcus Bleicher, CCAST- Workshop 2004

  11. Transverse mass spectra • Standard UrQMD and HSD underestimate the data • Additional resonances from 2-3 GeV do improve the description (UrQMD 2.1) Marcus Bleicher, CCAST- Workshop 2004

  12. Inverse slope systematics • Standard transport models fail • What is missing? • Maybe high mass resonanceslike in UrQMD 2.1 • Maybe QGP pressure… Marcus Bleicher, CCAST- Workshop 2004

  13. Phase diagram • QGP might be reachedalready at 11 GeV! • Tricritical point at 10-40 GeV • No phase transition at RHIC • Necessary to explore low energy region to study the phase transition Marcus Bleicher, CCAST- Workshop 2004

  14. Flow excitation functions: Summary • Standard transport models can not describe radial flow • Inclusion of high mass resonances leads to additional flow • Assumption of an early QGP phase might create additional flow Marcus Bleicher, CCAST- Workshop 2004

  15. Part II: Probing the late stage of the reaction: Resonances • Is there a (long living) hadronic rescattering stage at SPS and RHIC? • Lifetime of the hadronic stage is measured by resonance absorption/re-feeding • Use different resonances to explore this stage: e.g. mesons: baryons: • Are resonances dissolved in matter? Marcus Bleicher, CCAST- Workshop 2004

  16. π- ρ0 π+ ρ0 ρ0 ρ0 π- π+ π- ρ0 + + + π+ - - - Hadronic vs leptonic channel Au+Au Hot and dense medium Particle yields L* K K p Particle spectra p p L* time Marcus Bleicher, CCAST- Workshop 2004

  17. Statistical model fitting • Particle ratios well reproduced • Resonance ratios not reproduced(Braun-Munzinger, QM 2004) • too low • K*/K too high Braun-Munzinger et al. Marcus Bleicher, CCAST- Workshop 2004

  18. Yields and scaling in AA Baryon resonances: Meson resonances: All ratios a smooth, no sudden resonance disappearance Marcus Bleicher, CCAST- Workshop 2004

  19. Baryon resonances at RHIC All decaying resonances Finally observed resonances Signal loss due to rescattering of daughters Marcus Bleicher, CCAST- Workshop 2004

  20. Meson resonances at RHIC All decaying resonances Finally observed resonances Note that yields information about all decays (l.h.s), while yields information about r.h.s. Marcus Bleicher, CCAST- Workshop 2004

  21. What about the centrality dependence? • Where is the suppression? • K*/K deceases! • stays constant! Marcus Bleicher, CCAST- Workshop 2004

  22. Data vs. models Thermal model [1]: T = 177 MeV mB = 29 MeV Life time [fm/c] :  (1020) = 40 L(1520) = 13 K(892) = 4 ++ = 1.7 r (770) = 1.3 UrQMD [2] [1] P. Braun-Munzinger et.al., PLB 518(2001) 41 D.Magestro, private communication [2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker .Phys.G30 (2004) 111. Rescattering and refeeding are needed rather long living hadron stage Marcus Bleicher, CCAST- Workshop 2004

  23. Tch freeze-out Tkin freeze-out How can we understand these differences? • Strong decrease in kinetic freeze-out temperature from peripheral to central • Kinetic freeze-out as low as 80 - 90 MeV • Consequences for resonance re-feeding Marcus Bleicher, CCAST- Workshop 2004

  24. Estimate of re-feeding prob. Estimate of available energy for re-feeding at different reaction stages • can re-created until end of the reaction • re-creation is only possible near chemical freeze-out Marcus Bleicher, CCAST- Workshop 2004

  25. Decay time analysis • In the model rho mesons are not re-created after T=120 MeV.Check with mass shift.Check hadronic vs leptonicCheck centrality dependence • Deltas can be re-created until T=80-90 MeV.No centrality dependence Marcus Bleicher, CCAST- Workshop 2004

  26. Simple mass shift • Breit-Wiegner distr. for the rho mass • Fold with thermal distribution • Temperature dependent mass • For T=150-100 MeV the mass is shifted by 10-20 MeV downwards Marcus Bleicher, CCAST- Workshop 2004

  27. Rho mass shift predictions • Mass drops towards central reactions • Mass drops towards low pt Marcus Bleicher, CCAST- Workshop 2004

  28. Summary • K/ shows a peak around 20 GeV:-Peak can not be reproduced by transport models-Maybe sign of tri-critical point • Observed transverse flow is large:-Strength of flow can not be described in standard transport models-May be sign of early QGP formation-Maybe sign of high mass resonances • Resonances have been observed-Apparently no resonance dissolution-Statistical models fail to describe data-Strong re-feeding and absorption effects Marcus Bleicher, CCAST- Workshop 2004

  29. Thanks • Elena Bratkovskaya • Henning Weber • Christina Markert • Patricia Fachini • Manuel Reiter Marcus Bleicher, CCAST- Workshop 2004

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