Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland 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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland What was built and why? What has been accomplished? What is still to come? Plan

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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland * 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 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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland BRAHMS acceptance – run # 2

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

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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland FFS Hadron identification ++ p K+ 4 deg

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland FFS Hadron identification - C1 Cos  = 1/n  =>  th =1/n

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland BFS Hadron identification - RICH Low field run

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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland  s NN = 200 GeV Pseudorapidity densities of charged particles pppp BRAHMS: PRL 88 (2002)

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland  =4.5  =3.0 =0=0 p-p N_part

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland Centrality [%]  = 0  = 1.5  = 3.0  = 4.5 N ch N part 0 –           –                     –        8 90    –        6 64    –      9 95  9 30  4 43    * 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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland Saturation of excitation in fragmentation region Data shifted to the beam frame of reference BRAHMS: PRL 88 (2002)

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

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland Correlation – strange meson and baryon antiparticle-to-particle ratios BRAHMS: submitted to PRL, nucl-ex/

Zbigniew Majka M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland 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