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Title. 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. Plan. What was built and why? What has been accomplished?

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

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

  3. 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). Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl

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

  5. Tracking and PID • Forward Spectrometer • Full Forward Spectrometer (2.3o <  < 15o ) • 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 (15o <  < 30o ) • 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). Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl

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

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

  8. MRS Hadron identification - TOF m2=p2( t2 / L2 -1) Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl

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

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

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

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

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

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

  15. Pseudorapidity densities - comparison Centrality [%]  = 0 = 1.5  = 3.0  = 4.5 Nch Npart 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/R20) <p t >dN ch/d (where0 =1 fm/c, <p t > = 0.5 GeV/c) 5 GeV/fm3 (QGPcritical  1 GeV/fm3) Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl

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

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

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

  19. Summary from BRAHMS: The highest particle multiplicity observed in nuclear collisions ( Nch  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 Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland ufmajka@cyf-kr.edu.pl

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