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

2. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Outline of the Talk The BRAHMS experiment p T Spectra : slope systematic Rapidity distributions : K vs  Kaon and  B Conclusion

3. The BRAHMS Detector MRS FFS BFS

4. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Particle Identification TIME-OF-FLIGHT Particle Separation: p max ( 2  cut)= TOFWTOF1 TOF2  / K 2  cut K / p 2 GeV/c 3 GeV/c 4.5 GeV/c 3.5 GeV/c 5.5 GeV/c 7.5 GeV/c 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 CHERENKOV (2 settings)

5. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Kaon @ 200 GeV invariant differential yields Kaon @ 62.4 GeV invariant differential yields 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 Spectra Spectra : projection of rapidity intervals to p T axis

6. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Kaon Spectra Fit: exponential Top 5% central collisions AuAu 63 GeV AuAu 200 GeV

7. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Kaon Slopes Top 5% central collisions

8. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Integrated multiplicities @ 200 GeV (Gaussian fit) N(K + ) ~ 290 N(K  ) ~ 240 Rapidity Densities

9. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Rapidity Densities Width after Gaussian fit: AGS ~ no dependence SPS-RHIC ~ strong dependence : longitudinal flow important

10. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 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 Kaons vs Pions RAPIDITY DEPENDENCE

11. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 At y = 0, ratios converge to ~ 15 % ENERGY DEPENDENCE Why max AGS-SPS ? Net-Kaon distribution evolves like net-proton Over the full phase space: K + /  + = 16.6  1.5 % (syst) K  /   = 13.7  2.0 % (syst) Kaons vs Pions

12. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 ENERGY DEPENDENCE Kaons vs  B BRAHMS, PRL90 (2003) 102301 T~constant,  B varies with y Net-kaon and net-proton distributions at 3 different beam energies T~ constant,  B drives ratios in y or beam energy (?)

13. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 Summary & Conclusions Transverse momentum spectra of kaons measured in rapidity range -0.1 < y K < 3.4 for central Au+Au collisions at 200 and 63 GeV SLOPES: exponential in m T 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 to associated 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  B  B seems to drive the kaon ratio in rapidity and energy with T~ constant, preliminary 63 GeV data consistent with this

14. D. Ouerdane, Strange Quark Matter 2004, Cape Town, Sep. 15-20 The BRAHMS Collaboration I.G. Bearden 7, D. Beavis 1, C. Besliu 10, Y. Blyakhman 6, J.Brzychczyk 4, B. Budick 6, H. Bøggild 7, C. Chasman 1, C. H. Christensen 7, P. Christiansen 7, J.Cibor 4, R.Debbe 1, E. Enger 12, J. J. Gaardhøje 7, M. Germinario 7, K. Grotowski 4, K. Hagel 8, O. Hansen 7, A.K. Holme 12, H. Ito 11, E. Jacobsen 7, A. Jipa 10, J. I. Jordre 10, F. Jundt 2, C.E.Jørgensen 7, R. Karabowicz 4, T. Keutgen 9, E. J. Kim 5, T. Kozik 3, T.M.Larsen 12, J. H. Lee 1, Y. K.Lee 5, G. Løvhøjden 2, Z. Majka 3, A. Makeev 8, B. McBreen 1, M. Mikkelsen 12, M. Murray 8, J. Natowitz 8, B.S.Nielsen 7, K. Olchanski 1, D. Ouerdane 7, R.Planeta 4, F. Rami 2, D. Roehrich 9, B. H. Samset 12, D. Sandberg 7, S. J. Sanders 11, R.A.Sheetz 1, Z.Sosin 3, P. Staszel 7, T.S. Tveter 12, F.Videbæk 1, R. Wada 8, A.Wieloch 3 and I. S. Zgura 10 1 Brookhaven National Laboratory, USA, 2 IReS and Université Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland, 4 Institute of Nuclear Physics, Cracow, Poland 5 Johns Hopkins University, Baltimore, USA, 6 New York University, USA 7 Niels Bohr Institute, University of Copenhagen, Denmark 8 Texas A&M University, College Station. USA, 9 University of Bergen, Norway 10 University of Bucharest, Romania, 11 University of Kansas, Lawrence,USA 12 University of Oslo Norway