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Eun-Joo Kim University of Kansas For the BRAHMS collaboration
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  1. System and Rapidity Dependence of Baryon/Meson Ratios at RHIC Eun-Joo Kim University of Kansas For the BRAHMS collaboration

  2. Outline • The BRAHMS experiment • p/p ratios for different centrality bins • p/p ratios for different systems • p/p ratios at different rapidities • Summary

  3. Broad RAnge Hadron Magnetic Spectrometers • AuAu, CuCu, pp sNN= 200 GeV • MRS at 90o (y=0) and • full FS data at 4o (h~3.2) • PID by TFW2, C4,RICH

  4. Particle Identification MRS TFW2 FS RICH C4 • TFW2 : p/K ~ 2.5 GeV/c, K/p ~ 4.0 GeV/c with 2s cut • C4 : p/K ~ 9 GeV/c • RICH : p/K ~ 25 GeV/c, p ~ 35 GeV/c

  5. Centrality dependent pbar/p- ratios • Increase from peripheral to central in AuAu at sNN = 200 GeV • Ratio for peripheral AuAu approaches to pp • Ratios at forward rapidity turn over at lower pT than midrapidity BRAHMS Preliminary • No Anti-Lambda • Feed-Down Correction! • Errors are statistical only… pp at y~0 : PHENIX preliminary

  6. p/p increases with system size + -

  7. Comparison of AuAu & CuCu pbar/p- ratios are similar for different collision systems, and for a comparable number of binary collisions at y~0 and h~3.2

  8. p/p ratios in CuCu collisions + + - - Centrality dependence for p/p+ ratios is stronger at h~3.2 than y~0, but pbar/p- shows only slight centrality dependence at both rapidities.

  9. p/p+ ratios vs. <Npart> in CuCu pp p/p+ ratio integrated over 1.5<pT<2.5 GeV/c at forward rapidity increase with centrality; smaller dependence seen at midrapidity

  10. Rapidity and <Npart> dependence Strong rapidity dependence Y=0 h~3.2 pp pp

  11. Recombination & Coalescence Recombination and parton coalescence model describe ratios at midrapidty and suggest radial flow

  12. <pT> vs. rapidity and centrality AuAu sNN= 200 GeV y~0 Point : BRAHMS AuAu Curve : 3D Hydro (Hirano) Histo : AMPT PRC72,014908(2005) • <pT> decrease with y : p ~ 10%, p ~ flat from y=0 to y~3 • AMPT and 3D-Hydro model under-predict <pT> • 3D-Hydro describe y-dependence qualitatively • with a single Tth value (Tth = 100 MeV, Tch = 170 MeV)

  13. 3D-Hydro Model for AuAu BRAHMS Preliminary - p/p+ enhanced at forward rapidity, mainly from projectile? - Still high - Cronin, recombination, or flow? - The hydro calculation shown does not consider baryon nor isospin chemical potentials: There is no rapidity dependence. - Particle ratio is fixed at chemical freezeout temperature PHENIX : PRC69,034909(2004)

  14. Summary • BRAHMS has studied the pT/centrality/rapidity/system dependence of the p/p ratios for AuAu, CuCu and pp - p/p ratios are enhanced in AA collisions compared to pp - No other system dependence is observed - p/p+ and pbar/p- ratios show similar interplay between soft and hard processes for different systems - However, there is strong rapidity dependence (baryo-chemical potential?) • (p/p ratio)/<Npart> at constant h independent of system

  15. The BRAHMS Collaboration I.Arsene9,11, I.G. Bearden6, D. Beavis1, S.Bekele10, C. Besliu9, B. Budick5, H. Bøggild6, C. Chasman1, C. H. Christensen6, P. Christiansen6, R.Clarke9, R.Debbe1, J. J. Gaardhøje6, K. Hagel7, H. Ito1, A. Jipa9, J. I. Jordre8, F. Jundt2, E.B.Johnson10, J.I.Jordre8, C.Jørgensen6, R. Karabowicz3, E. J. Kim10, T.M.Larsen6, J. H. Lee1, Y. K.Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3 , M. Murray10, J. Natowitz7, B.S.Nielsen6, D.Ouerdane6, R.Planeta3, F. Rami2, C.Ristea6, O.Ristea9, D. Röhrich8, B. H. Samset11, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7, H.Yang8, Z. Yin8,and I. S. Zgura9 1Brookhaven National Laboratory, USA 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Krakow, Poland 4Johns Hopkins University, Baltimore, USA 5New York University, USA 6Niels Bohr Institute, University of Copenhagen, Denmark 7Texas A&M University, College Station. USA, 8University of Bergen, Norway 9University of Bucharest, Romania 10University of Kansas, Lawrence,USA 11University of Oslo, Norway 48 physicists from 11 institutions

  16. Corrections in AuAu

  17. Net-p distributions? Dynamics for Baryon/Meson is similar to p/p+ and pbar/p-?

  18. p/p+ ratios on Ncoll