Zbigniew MajkaM.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 MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
•What was built and why?
•What has been accomplished?
•What is still to come?
Plan
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
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 MajkaM.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 MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
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).
Tracking and PID
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
BRAHMS acceptance – run # 2
Zbigniew MajkaM.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 MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
MRS Hadron identification - TOF
m2=p2( t2 / L2 -1)
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
FFS Hadron identification
+
p
K+
4 deg
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
FFS Hadron identification - C1
Cos = 1/n => th=1/n
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
BFS Hadron identification - RICH
Low field run
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
sNN = 130 GeV
BRAHMS: PRL 87 (2001) 112305 BRAHMS: PL B523 (2001) 227
•Rapidity dependence of antiparticle-to-particle ratio
•Pseudorapidity densities of charged particles
•Comparison with models
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
sNN = 200 GeV
Pseudorapidity densities of charged particles
pp
BRAHMS: PRL 88 (2002) 202301
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
=4.5
=3.0
=0
p-p
N_part
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
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/R20) <p t >dN ch/d
(where 0 =1 fm/c, <p t > = 0.5 GeV/c) 5 GeV/fm3
(QGPcritical 1 GeV/fm3)
Pseudorapidity densities - comparison
Zbigniew MajkaM.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) 202301
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
Antiparticle-to-particle ratio:
- vs rapidity
130 GeV
- centrality and pt dependence
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
Correlation –strange meson and baryon antiparticle-to-particle ratios
BRAHMS: submitted to PRL, nucl-ex/0207006
Zbigniew MajkaM.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
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
