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Hyperon production in Pb+Pb collisions @

Hyperon production in Pb+Pb collisions @. SPS. Christine Meurer J. W. Goethe-Universit ät / Frankfurt for the NA49 collaboration. Outline. New data: X and W at 40AGeV, L at 30AGeV Transverse distribution Longitudinal distribution Energy dependence of hyperon production

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Hyperon production in Pb+Pb collisions @

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  1. Hyperon production in Pb+Pb collisions@ SPS Christine Meurer J. W. Goethe-Universität /Frankfurt for the NA49 collaboration

  2. Outline • New data: X and W at 40AGeV, L at 30AGeV • Transverse distribution • Longitudinal distribution • Energy dependence of hyperon production • Centrality dependence of X- production at 40AGeV • Summary and Outlook Christine Meurer for NA49

  3. New data Entries L • L at 30 AGeV • X and W at 40 AGeV minv (GeV/c2) Entries Entries minv (GeV/c2) minv (GeV/c2) Christine Meurer for NA49

  4. Transverse distribution: mT –spectra 40 AGeV 158 AGeV Exponential fit does notdescribe spectra very well at low and high mT range. Pb+Pb (7%) Pb+Pb (10%) preliminary preliminary 20% L, X,W • L at 40 and 158AGeV: nucl-ex/0311024 • at 158AGeV: Phys. Lett. B 538 (2002) 275 W at 158AGeV: Nucl. Phys. A 715 (2003) 161c Spectra at mid-rapidity Fit range: 0.2-1.4 Christine Meurer for NA49

  5. Transverse distribution: mass dependence of T p KpfL X W preliminary • Light particles show a linear increase of T with mass. • For heavier particles T seems to saturate, but on different levels for different energies. Open symbols: antiparticles Christine Meurer for NA49

  6. Transverse distribution: blast wave fit Radial flow fit: r = atanh bT Schnedermann, Sollfrank, Heinz Phys. Rev. C 48 (1993) 2462 preliminary Good description of the spectra, also for low mT range. preliminary Similar parameters for both energy. Same procedure for K- and K+ Christine Meurer for NA49

  7. Transverse distribution: blast wave fit parameters preliminary preliminary 40 AGeV: Slight differences of the parameters for X+W and for K-+K+ 158 AGeV: Similar parameters No evidence for early decoupling of X and W Christine Meurer for NA49

  8. Longitudinal distribution: rapidity spectra 40 AGeV 30 AGeV 80 AGeV 158 AGeV preliminary preliminary preliminary L, X,W • A clear evolution of shape of L is visible. • No big change of shape of X and W with energy. sys. error ~ 10% Christine Meurer for NA49

  9. Energy dependence of hyperon production 4p yields • Ls show a distinct maximum at 30AGeV. • For Xs and Ws a weak maximum is indicated. x6 preliminary x 6 x15 x 15 Y = L, X-, W-+W+ AGS data: E895 Hadron-gas model: Braun-Munzinger, Cleymans, Öschler, Redlich Nucl. Phys. A697 (2002) 902 Christine Meurer for NA49

  10. Energy dependence of B/B at mid-rapidity Energy dependence of B/B changes with strangeness content of the particles. preliminary Christine Meurer for NA49

  11. Centrality dependence of X- at 40AGeV At 40AGeV the X--production shows a saturation effect from mid-central to central reactions. preliminary See also: “System size dependence” poster at this conference presented by Ingrid Kraus Christine Meurer for NA49

  12. Summary • New data: X,W at 40AGeV, L at 30AGeV in Pb+Pb collisions • Transverse distributions: • Mt-spectra: no good description by exponential fit but by blast wave fit • No evidence of early decoupling of X and W • Longitudinal distributions: • Rapidity spectra: clear evolution of shape of L from 30 to 158AGeV, Gausian shape for X and W at 40 and 158AGeV • Energy dependence: • Distinct maximum at 30AGeV for L/p-,weak maximum for X/p- and W/p- • B/B-ratio: energy dependence changes with strangeness content • Centrality dependence of X-/NW at 40AGeV: • Increase from peripheral to mid-central and followed by saturation • Outlook: • Complete analysis of hyperons with data at 20, 30, 40, 80, and 158AGeV Christine Meurer for NA49

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