1. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Review of early results from BRAHMS experiment at RHIC Zbigniew Majka (for the BRAHMS Collaboration) Department of Hot Matter Physics, M. Smoluchowski Institute of Physics Jagiellonian University, Kraków, Poland Title

2. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl What was built and why? What has been accomplished? What is still to come? Plan

3. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl BRAHMS Experimental setup *Measurements: p, K,  identified over wide range of rapidity: 0 < |y| < 4 0.2 < pt < ~ 3GeV/c central and fragmentation region vs centrality (with high precision).

4. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl * Results address: Baryon stopping. Reaction mechanism and dynamics Chemical equilibrium Thermalization Baryo-chemical potential Particle production Particle to antiparticle ratios Mini-jet production

5. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Forward Spectrometer Full Forward Spectrometer (2.3 o <  < 15 o ) High-momentum mode –sweeping D1,D2 –tracking and momentum determination by T2-T5, D3,D4 –PID: RICH (  /K/p) separation < 25 GeV/c –Tof-H2 (  /K < 5, K/p < 8.5 GeV/c with 4  cut) Low-momentum mode –tracking and momentum determination by T1-T2, D2 –PID: C1 (  /K) separation < 9 GeV/c –Tof-H1 (  /K < 3.3, K/p < 5.7 GeV/c with 4  cut Front Forward Spectrometer (15 o <  < 30 o ) –Same as Low-momentum Mode Momentum resolution  (dp/p) ~ 1% Mid-Rapidity Spectrometer Tracking and Momentum determination, MTP1,MTP2 and D5. PID TOFW (  /K < 2.2, K/p < 3.7 GeV/c with 4  cut). Tracking and PID

6. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl BRAHMS acceptance – run # 2

7. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl SiMA (2.0< |  |<2.0) PTMA (2.2< |  | <2.2) BBC (3 < |  | < 4) Centrality determination – vertex distribution Silicon Strips Plastic Scintillator Tiles Beam–Beam

8. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl MRS Hadron identification - TOF m 2 =p 2 ( t 2 / L 2 -1)

9. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl FFS Hadron identification ++ p K+ 4 deg

10. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl FFS Hadron identification - C1 Cos  = 1/n  =>  th =1/n

11. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl BFS Hadron identification - RICH Low field run

12. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl  s NN = 130 GeV BRAHMS: PRL 87 (2001) 112305BRAHMS: PL B523 (2001) 227 Rapidity dependence of antiparticle-to-particle ratio Pseudorapidity densities of charged particles Comparison with models

13. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl  s NN = 200 GeV Pseudorapidity densities of charged particles pppp BRAHMS: PRL 88 (2002) 202301

14. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl  =4.5  =3.0 =0=0 p-p N_part

15. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Centrality [%]  = 0  = 1.5  = 3.0  = 4.5 N ch N part 0 – 5 553  36 625  55 554  37 627  54 372  37 470  44 107  15 181  22 3860  300 4630  370 352 346 5 – 10 447  29 501  44 454  31 515  48 312  36 397  37 94  13 156  18 3180  250 3810  300 299 293 10 - 20 345  23 377  33 348  25 386  35 243  27 309  28 79  10 125  14 2470  190 2920  230 235 228 20 – 30 237  16 257  23 239  16 267  23 172  18 216  17 59  8 90  10 1720  130 2020  160 165 164 30 – 40 156  11 174  16 159  11 182  16 117  13 149  14 43  6 64  7 1160  90 1380  110 114 114 40 – 50 98  7 110  10 104  7 115  11 77  9 95  9 30  4 43  5 750  60 890  70 75 76 * 4630 charged particles produced for 0-5% central * 14% increase over 130GeV * 50% increase over p +  p (UA5) => significant medium effects Bjorken energy density:  BJ = (1/  R 2  0 ) dN ch /d  (where  0 =1 fm/c, = 0.5 GeV/c)  5 GeV/fm 3 (  QGP critical  1 GeV/fm 3 ) Pseudorapidity densities - comparison

16. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Saturation of excitation in fragmentation region Data shifted to the beam frame of reference BRAHMS: PRL 88 (2002) 202301

17. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Antiparticle-to-particle ratio: - vs rapidity 130 GeV - centrality and p t dependence

18. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Correlation – strange meson and baryon antiparticle-to-particle ratios BRAHMS: submitted to PRL, nucl-ex/0207006

19. Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl Summary from BRAHMS: The highest particle multiplicity observed in nuclear collisions ( N ch  4600) Large(st) energy density (   5  crit ) High reaction transparency (p-/p+  0.75 at y=0) Decoupling between central and ’fragmentation’ regions Onset of boost invariant plateau Preliminary: Partonic (color) description appears necessary Central region dominated by matter-antimatter balance: Qualitatively new physics regime Tranverse flow at y=0 not significantly different from SPS? Moderate transverse source sizes