1. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim Parton energy loss, saturation, and recombination at BRAHMS Eun-Joo Kim University of Kansas For the BRAHMS collaboration

2. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim Hard scattering at RHIC Hard scattering at RHIC modifications study modifications of high p T production in AA, dA with respect to pp via N coll scaling to learn about QCD dynamics : QGPCG C Quark Gluon Plasma and/or Color Glass Condensate R AA = (yield AA / )/yield pp R cp = (yield central / cent )/(yield peripheral / peripheral ) coalescence recombination

3. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim  Parton dynamics in a dense system of gluons differs from pQCD  parton saturation CGC  Color Glass Condensate (effective field theory of dense gluon systems) controls gluon density in hadron hadron collisions  initial conditions for QGP the QGP ? Evolution & Saturation

4. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim BRAHMS Broad RAnge Hadron Magnetic Spectrometers

5. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim Experimental observations R dAu : enhancement Au+Au  R AuAu & R cp ~ suppression  strong effect of dense medium   dependence ?  baryon-meson ~ different behavior BRAHMS preliminary BRAHMS PRL91(2003)072305 Au+Au Rapidity dependence Particle dependence

6. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim Rapidity dependant R dAu, R cp BRAHMS PRL93(2004)242303 Cronin like enhancement increasing suppression centrality dependence reversed at forward rapidities consistent with CGC prediction : PLB599(2004) 23

7. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim But… Recombination also works! But… Recombination also works! with only the recombination of soft and shower partons no multiple scattering, or gluon saturation put in explicitly Hwa & Yang : nucl-th/04010111 BRAHMS dAu data PRL93(2004) 242303  =2.2  =3.2 d+Au

8. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim R AA for identified hadrons  =2.2 BRAHMS preliminary   - : strong suppression at  ~0 & 2.2 in AuAu  p : enhanced at  ~2.2(AuAu), 3.2(dAu) collisions Au+Aud+Au

9. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim peripheral collision  pp collision R cp for identified hadrons in AuAu BRAHMS preliminary R cp for  -, K -, p at y~3.2 at p T ~ 2GeV/c  Mass (or Baryon-Meson) dependent R cp  Stronger centrality dependence for   “Still” significant quark recombination at y~3.2 ? Y~3.2

10. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim 40-60%20-40%10-20%0-10% Energy dependence (SPS  RHIC) p T = 3-4 GeV/c R AuAu at  s NN = 62.4GeV BRAHMS preliminary  ~0.95 Suppression?

11. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim p/  Ratios in AuAu p/  Ratios in AuAu BRAHMS : Preliminary PHENIX : PRC69(2004) 034909 Hwa & Yang : PRC70(2004) 024905 Greco & Ko, PRC68(2003) 034904  p/  - ratios lower at forward rapidity while suppression persists?  no significant difference between y=0 and y~1  flow/mass effect ? Hwa & Yang : y=0 Greco & Ko : y=0

12. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim Ratios at  ~3.2 in dAu, pp roughly as many protons as pions at high p T at forward rapidity in dAu indicate other processes besides parton fragmentation significant difference small excess

13. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim summary  BRAHMS has measured rapidity dependent nuclear modification factors and particle ratios in AuAu, dAu, and pp collisions.  In AuAu collisions at  s NN =200GeV, - High p T suppression (mesons) observed at y ~ 0, 2.2, and 3.2. - No strong rapidity dependent suppression. - Suppression is smooth with energy at 63, 130, and 200GeV.  In dAu collisions at  s NN =200GeV, - significant reduction of the nuclear modification factor at forward rapidity and this suppression increases with  and the centrality.  Initial state can be described by parton saturation (CGC).  Baryon vs. Meson : Production and Nuclear Modification - Recombination/Coalescence can give reasonable explanation at intermediate p T in AuAu and dAu collisions.

14. 20-26 Feb. 2005 Lake Louise Eun-Joo Kim I.Arsene 10, I. G. Bearden 7, D. Beavis 1, C. Besliu 10, B. Budick 6, H. Bøggild 7, C. Chasman 1, C.H.Christensen 7,P. Christiansen 7, J. Cibor 3, R. Debbe 1, E. Enger 12, J. J. Gaardhøje 7, M. Germinario 7, K. Hagel 8, H. Ito 1, A.Jipa 10, F. Jundt 2, J. I. Jørdre 9, C. E. Jørgensen 7, R. Karabowicz 4, E. J. Kim 1,11, T. Kozik 4,T. M. Larsen 12, J. H. Lee 1, Y. K. Lee 5, S. Lindal 12, R. Lystad 9, G. Løvhøiden 12, Z. Majka 4, A. Makeev 8, M. Mikelsen 12, M. Murray 8, 11, J. Natowitz 8, B. Neumann 11, B. S. Nielsen 7, D. Ouerdane 7, R. Planeta 4, F. Rami 2, C. Ristea 10, O. Ristea 10, D. Röhrich 9, B. H. Samset 12, D. Sandberg 7, S. J. Sanders 11, R. A. Scheetz 1, P. Staszel 7, T. S. Tveter 12, F. Videbæk 1, R. Wada 8, Z. Yin 9, I. S. Zgura 10 1 Brookhaven National Laboratory, Upton, New York, USA 2 IReS and Université Louis Pasteur, Strasbourg, France 3 Institute of Nuclear Physics, Krakow, Poland 4 Smoluchkowski Inst. Of Physics, Jagiellonian University, Krakow, Poland 5 Johns Hopkins University, Baltimore, USA 6 New York University, New York, USA 7 Niels Bohr Institute, University of Copenhagen, Denmark 8 Texas A & M University, College Station, Texas, USA 9 University of Bergen, Bergen, Norway 10 University of Bucharest, Romania 11 University of Kansas, Lawrence, Kansas, USA 12 University of Oslo, Oslo, Norway The BRAHMS Collaboration