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Kaon Production in Central Au+Au Collisions at 200 and 63 GeV

Kaon Production in Central Au+Au Collisions at 200 and 63 GeV. BRAHMS. Djamel Ouerdane Niels Bohr Institute for the BRAHMS Collaboration. Strange Quark Matter 2004 Cape Town, September 15-20. Outline of the Talk. The BRAHMS experiment p T Spectra : slope systematic

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Kaon Production in Central Au+Au Collisions at 200 and 63 GeV

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  1. Kaon Production in Central Au+Au Collisions at 200 and 63 GeV BRAHMS Djamel Ouerdane Niels Bohr Institute for the BRAHMS Collaboration Strange Quark Matter 2004 Cape Town, September 15-20

  2. Outline of the Talk • The BRAHMS experiment • pT Spectra : slope systematic • Rapidity distributions : K vs  • Kaon and B • Conclusion

  3. The BRAHMS Detector MRS FFS BFS

  4. Particle Identification CHERENKOV RICH: Cherenkov light focused on spherical mirror  ring on image plane Ring radius vs momentum gives PID  / K separation 20 GeV/c Proton ID up to 35 GeV/c (2 settings) TIME-OF-FLIGHT Particle Separation: pmax (2 cut)= 2 cut TOFW TOF1 TOF2  / K 3 GeV/c 4.5 GeV/c 2 GeV/c K / p 3.5GeV/c 5.5GeV/c 7.5GeV/c

  5. Kaon Spectra By combining all data sets and averaging over the number of collisions, we get the final invariant yields over a broad range of phase-space Kaon @ 200 GeV invariant differential yields Kaon@ 62.4 GeV invariant differential yields Spectra : projection of rapidity intervals to pT axis

  6. Kaon Spectra Fit: exponential Top 5% central collisions AuAu 200 GeV AuAu 63 GeV

  7. Kaon Slopes Top 5% central collisions

  8. Rapidity Densities Integrated multiplicities @ 200 GeV (Gaussian fit) N(K+) ~ 290 N(K) ~ 240

  9. Rapidity Densities Width after Gaussian fit: AGS ~ no dependence SPS-RHIC ~ strong dependence : longitudinal flow important

  10. Kaons vs Pions Y < 1 : consistent with Hadron Gas Stat. Model K+/+ : 15.6  0.1 % (stat) K/ : 14.7  0.1 % (stat) [Phys. Lett. B 518 (2001) 41] Divergence at higher y : Associated K+ production No single source with unique T and B RAPIDITY DEPENDENCE

  11. Kaons vs Pions Over the full phase space: K+/+ = 16.6  1.5 % (syst) K/ = 13.7  2.0 % (syst) Why max AGS-SPS ? Net-Kaon distribution evolves like net-proton ENERGY DEPENDENCE At y = 0, ratios converge to ~ 15 %

  12. Kaons vs mB BRAHMS, PRL90 (2003) 102301 T~constant, Bvaries with y T~ constant, mB drives ratios in y or beam energy (?) ENERGY DEPENDENCE Net-kaon and net-proton distributions at 3 different beam energies

  13. Summary & Conclusions Transverse momentum spectra of kaons measured in rapidity range -0.1 < yK < 3.4 for central Au+Au collisions at 200 and 63 GeV SLOPES: exponential in mT gives good description slopes at 200 GeV > 63 GeV, small step  YIELDS: N(+) ~ N(-) at mid-rapidity (47 and 44) but N(+) > N(-) at y > 2 due toassociated K+ production K /  converge to ~ 15% at y ~ 0 (plateau y < 1) same within systematic errors for full phase-space ratios possible indication of strangeness equilibration at 200 GeV At 63 GeV, y = 0, ratios at “expected” values K vs mBmB seems to drive the kaon ratio in rapidity and energy with T~ constant, preliminary 63 GeV data consistent with this

  14. The BRAHMS Collaboration I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6, H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, E. Enger12, J. J. Gaardhøje7, M. Germinario7, K. Grotowski4 , K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, C.E.Jørgensen7, R. Karabowicz4 , T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Mikkelsen12, M. Murray8, J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9, B. H. Samset12, D. Sandberg7, S. J. Sanders11, R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8, A.Wieloch3 and I. S. Zgura10 1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland 5Johns Hopkins University, Baltimore, USA, 6New York University, USA 7Niels Bohr Institute, University of Copenhagen, Denmark 8Texas A&M University, College Station. USA, 9University of Bergen, Norway 10University of Bucharest, Romania,11University of Kansas, Lawrence,USA 12 University of Oslo Norway

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