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Transport Model Analysis of Ultra-Relativistic AA interactions

Transport Model Analysis of Ultra-Relativistic AA interactions. Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany. Thanks to. Elena Bratkovskaya Sascha Vogel Xianglei Zhu Stephane Haussler Hannah Petersen Diana Schumacher. Contents.

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Transport Model Analysis of Ultra-Relativistic AA interactions

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  1. Transport Model Analysis of Ultra-Relativistic AA interactions Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany Marcus Bleicher, APFB05, SUT Thailand

  2. Thanks to • Elena Bratkovskaya • Sascha Vogel • Xianglei Zhu • Stephane Haussler • Hannah Petersen • Diana Schumacher Marcus Bleicher, APFB05, SUT Thailand

  3. Contents • Introduction • Strangeness as QGP signal • Experimental facts: the ‘horn’ • Strange fluctuations • Summary Marcus Bleicher, APFB05, SUT Thailand

  4. 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 (not in v1.3) • Generates full space-time dynamics of hadrons and strings Marcus Bleicher, APFB05, SUT Thailand

  5. Collision Spectrum 1fm/c 10fm/c • Initial stage scattering before 1.5 fm/c: Baryon stopping, meson production, • Thermalization stage (1.5 – 6 fm/c): Cooking QCD matter, may be QGP formation • Hadronic freeze-out stage (6 – 10 fm/c): Elastic and pseudo-elastic hadron scatterings Pb+Pb @ 160 AGeV Marcus Bleicher, APFB05, SUT Thailand

  6. Where do we expect QGP? • 1st Order phase transition at high • No P.T. at low • Search for irregularities around Ebeam = 10-40 GeV: • Flow, strangeness, E-by-E Plot adapted from L. Bravina Marcus Bleicher, APFB05, SUT Thailand

  7. Strangeness enhancement T~0.2-0.3 GeV  QGP has lower threshold for strangeness production  relative strangeness enhancement Marcus Bleicher, APFB05, SUT Thailand

  8. PP Excitation functions • PP works nicely • Perturbative QCD is used for hard scatterings above 50 GeV Marcus Bleicher, APFB05, SUT Thailand

  9. AA Excitation functions • 4 and mid-y abundancies: OK • Energy dependence: OK • Hadron-string models work well Marcus Bleicher, APFB05, SUT Thailand

  10. Excitation functions: ratios • ‘Horn’ in the ratio not reproduced • well reproduced • relative strange baryon enhancement reproduced Marcus Bleicher, APFB05, SUT Thailand

  11. Fluctuation studies: Ratios • 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, APFB05, SUT Thailand

  12. Baryon-Strangeness Correlations I Definition: Idea: Strangeness and baryon numbercarriers are different in QGP and hadron gas. First suggested by V. Koch et al., 2005 • HG: strangeness is decoupled from baryon number (mesons)  small CBS correlation • QGP: strangeness is fixed to baryon number (strange quark) large CBS correlation Marcus Bleicher, APFB05, SUT Thailand

  13. Baryon-Strangeness Correlations 2 • Limiting cases for CBS: • Large mB: CBS3/2 • large acc. window: CBS0Explored with help of increasing rapidity window inAu+Au reaction at RHIC • Present models yield similar results for small rapidity window • Different handling of the fragmentation region/spectators influences results at large rapidities Marcus Bleicher, APFB05, SUT Thailand

  14. Baryon-Strangeness Correlations 3 Energy dependence of CBS allows to study the onset of deconfinement transition Note that the QGP result is for m=0 Here |ymax|<0.5 • Deviations from the HG are expected around high SPS energy region, due to QGP onset. Marcus Bleicher, APFB05, SUT Thailand

  15. Baryon-Strangeness Correlations 4 Centrality dependence of CBS allows to study the critical volume needed for QGP formation. Note that the QGP result is for m=0 |ymax|<0.5, Ecm=200AGeV • Hadron-string transport models predict no centrality dependence of CBS • A QGP transition leads to a strong centrality dependence Marcus Bleicher, APFB05, SUT Thailand

  16. Summary • Hadron yields are well reproduced in models • Most ratios can be understood in transport models • Model K+/p+ ratios do not reproduce the strong peak observed in data • In data, the dynamical fluctuation of K/p increase strongly towards 20 AGeV beam energy (not present in hadron-string models) • Baryon-strangeness correlations allow to pin down the onset of the QGP transition. Marcus Bleicher, APFB05, SUT Thailand

  17. Conclusion Most interesting energy range, because: • K/p ratio enhanced • Large dynamical fluctuations • Latent heat is big Will be explored by new GSI accelerator (near Frankfurt) Marcus Bleicher, APFB05, SUT Thailand

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