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X - and X + production in Pb+Pb collisions at 40A  GeV at SPS

X - and X + production in Pb+Pb collisions at 40A  GeV at SPS. Christine Meurer J.-W.-Goethe-Universität Frankfurt/Main for the NA49 collaboration. 1. Outline. Motivation NA49 experiment Analyzed data sets and centrality bins X –analysis Results:

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X - and X + production in Pb+Pb collisions at 40A  GeV at SPS

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  1. X-and X+production in Pb+Pb collisions at 40AGeV at SPS Christine Meurer J.-W.-Goethe-Universität Frankfurt/Main for the NA49 collaboration

  2. 1. Outline • Motivation • NA49 experiment • Analyzed data sets and centrality bins • X –analysis • Results: • Centrality dependence of X+/X--ratio • Energy dependence of X+/X--ratio • Summary and outlook Christine Meurer

  3. 2. Motivation • Measurement of multiple strange particles provide important information on hadronization features of heavy ion collisions • Looking for qualitative changes (onset phenomena), when varying: • System size • Energy density • Study of X -production as function of: • Collision centrality • Beam energy • X+/X-–ratio reflects changes in baryon density Christine Meurer

  4. 3. NA49 experiment Veto-Calorimeter for centrality selection Christine Meurer

  5. 4. Analyzed data sets • Pb+Pb (minimum bias) at 40AGeV • (Pb+Pb (7% most central) at 40AGeV, Nevt = 700,000, still to be analysed) 1 2 3 4 5 6 central  peripheral Christine Meurer

  6. Geometrical cuts are used to reduce the background: Impact parameter of X Impact parameter of L Decay position of X Proton selection by dE/dx 5. X-analysis Invariant mass-spectra at mid-rapidity X-mass = 1.321 Christine Meurer

  7. 6. Phase space population 1.–4. centrality bin: Measured X- pt > 0.3 5.+6. centrality bin: pt > 0.0 mid-rapidity = 2.2 Christine Meurer

  8. 7. Invariant mass spectra at mid-rapidity central mid central peripheral X- X+ Christine Meurer

  9. 8. Centrality dependence of X+/X--ratio • The X+/X--ratio has only a weak centrality dependence at 40AGeV preliminary Christine Meurer

  10. 9. Energy dependence of X+/X--ratio • The X+/X--ratio increases with the energy • All ratios at mid-rapidity • All ratios for central collisions • Reflecting decreasing baryon density preliminary Christine Meurer

  11. 10. Hadron-gas model (F. Becattini et al.) • The HG model (with partial strangeness saturation) predicts: X+/X-= 0.06 (4p) • Measured: X+/X-= 0.11 ± 0.02 (mid-rapidity) Close to hadron-gas model prediction Christine Meurer

  12. 11. Summary and outlook • First results on centrality dependence of Xs at 40AGeV from NA49: • Weak centrality dependence of X+/X--ratio • The X+/X- -ratio increases with the energy • Measured X+/X--ratio is close to the hadron-gas model • Outlook: • Corrected spectra for X- and X+ at 40AGeV • 4p yields (40AGeV) • X-analysis at 20,30 and 80AGeV Christine Meurer

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