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The Latest Results from PHOBOS. Charged-Particle Multiplicity and Particle Ratios in Au + Au Collisions at RHIC Energies Using the PHOBOS Detector. Rachid Nouicer University of Illinois at Chicago for the Collaboration. The PHOBOS Collaboration. ~ 70 collaborators. - PowerPoint PPT Presentation
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-1- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Charged-Particle Multiplicity and Particle Ratiosin Au + Au Collisions at RHIC Energies
Using the PHOBOS Detector
The Latest Results from PHOBOS
Rachid Nouicer
University of Illinois at Chicago
for the Collaboration
-2- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
The PHOBOS Collaboration
Argonne National LaboratoryBrookhaven National Laboratory
Institute of Nuclear Physics KrakowMassachusetts Institute of TechnologyNational Central University, Taiwan
University of Rochester University of Illinois at Chicago
University of Maryland
~ 70 collaborators
-3- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Completed Spring 2001 •4 Multiplicity Array
- Octagon, Vertex & Ring Counters• Two Mid-rapidity Spectrometers• TOF wall for High-Momentum PID• Triggering
-Scintillator Paddles + Cerenkov Counters- Zero Degree Calorimeter 135000 Silicon Pad channels
PHOBOS Apparatus
-4- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Collisions at 200 GeV!
Single Event in PHOBOS
-5- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Sample Silicon pad sizesOctagon Detector: 2.7 x 8.8 mm2
Vertex Detector: 0.4 x 12 mm2
Ring Counter: 20 -106mm2
Spectrometer: 1 x 1 mm2
Ring Counter
Octagon Detector
Vertex Detector
Spectrometer
PHOBOS Silicon Detector
-6- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Silicon Detector Performance
dE/dx resolution = 6.9%
K
p
d• Signal is well reproduced by MC• Signal/Noise ~ 14 to 20 • Particles are well identified by spectrometer within 2T magnetic field
-7- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Triggering on Collisions & Centrality Negativ
e Paddles
Positive Paddles
Au Aux
z
PPPN
Positive ZDC
Negative ZDC
NegativeCerenkov
PositiveCerenkov
Paddle signal (a.u.)
ZD
C S
ign
al (
a.u
.)
Npart
Nsp
ect
ato
r=2
A-N
part
Central
Peripheral
200 GeV Data • Coincidence between Paddle counters
at t = 0 defines a valid collision
• Paddle + ZDC timing reject background
• Trigger sensitive to 97% of inelastic cross section
Measurement
-8- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Single-event display
Vertex “tracklets” – 3 point tracks
1
-5.4<<5.4
Multiplicity Measurements in 4
-9- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
56 & 130 GeV : PRL 85, 3100(2000) 200 GeV : PRL 88, 22302(2002)
Charged Particle Multiplicity near Mid-rapidity vs Energy
Results :
Central
Extrapolation to LHC : E(LHC)=30 E(RHIC)
2200) dN/dη LHC ( - KN Saturation Model :
1300 ) dN/dη ( LHC - A + A Fit :
Model prediction :
• no unexpected increase• 200 GeV AuAu 55% higher than pp
• dN/d = 650 +/- 35
for AuAu at 200 GeV (6% central)
hep-ph/0111315
PHOBOS : AuAu at RHIC
-10- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
PHOBOS : 130 GeV : PRC 65, 031901(2002)PHOBOS : 200 GeV submitted to PRC Saturation Model : nucl-th/0108006
Central Peripheral
Centrality Dependence & Comparison to Models Results
Two-component Fit :
dN/d= (1-x)nppNpart/2 + xnppNcoll
“soft” “hard”
0.02 1 0.1 2.42 GeV 200
0.02 0.09 2.23 GeV 130
x n Energy pp
|| < 1
PHOBOS : AuAu at RHIC
1.34(130) hard(200) hard
1.07 (130) soft(200) soft
-11- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
dN/d
dN/d
dN/d
dN
/d
dN/d
dN/d
Results : Charged Particle Production vs Au+Au at 200 GeV : latest results
AuAu at 130 GeV : PHOBOS PRL 87, 102303 (2001)
200 GeV130 GeV
Central
Peripheral
Systematic Errors
-12- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Energy Dependence & Comparison to pp
Most central
Width Increases with Ecm
Au+Au & pp at 200 GeV A+A
Results :
HI Particle Production is Increased at Mid-Rapidity
RHIC : PHOBOS AuAu s = 200 GeV
SPS : EMU-13 PbPb s = 17 GeV RHIC : PHOBOS AuAu s = 130 GeV
Systematic errors not included
-13- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Results : Limiting Fragmentation
Fragmentation
A+A
p + p UA5, Z.Phys.C33, 1 (1986)
AuAu and pp show the same behavior, the extent of the fragmentation region grows with collision energy
Fragmentation
Systematic errors not included
-14- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Results : Limiting Fragmentation vs Centrality
• The extent of the limiting fragmentation region is independent of centrality
but the shape in this region depends on centrality !
200 GeV 200 GeV
200 GeV Data 130 GeV Data
130 GeV130 GeV
Fragmentation Fragmentation
-15- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Anti-particle / particle ratios
• Tracking in the spectrometer• Alternate 2T magnetic fields• Energy loss and momentum
+
K-
p
-
p
K+
+
Positive
Charge
Negative
Charge
-16- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
AuAu130 GeV
Central region not Baryon-Free
Centrality =12 %<Npart> ~ 310
PHOBOS : Phys.Rev.Lett. 87, 102301(2001)
Stat. Syst.
K. Redlich, Quark Matter 2001
Results : Anti-particle/particle ratios
06.004.060.0
06.007.091.0
02.001.000.1
p
p
K
K
T= 170 MeV
-17- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Compare to Lower Energy
PHOBOS : 130 GeV Phys. Rev. Lett. 87, 102301 (2001)
/KK - p/p
Results :
Antiproton/proton ratio Increasing towards unity (baryon free)
PHOBOS
-18- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
• dNch/d @ | per participant• AuAu 55% higher yield than pp at maximum RHIC energy• Npart >100 the R200/130 approximately constant at 1.14 +/- 0.01+/- 0.06
• AuAu data at 200 & 130 GeV are in good agreement with parton saturation model predictions and the two-component fits to the data (hard + soft)
• Using the two-component fits the hard processes increase by 34 % and the soft by 7 % from 130 to 200 GeV in AuAu
• dNch/d in 4• 200 GeV : <Nch> = 4960 +/- 250 (||< 5.4) for 6% central
• Additional particle production near | for central events• Central AuAu has very similar shape to pp • Extent of fragmentation region grows with collision energy
• Particle ratios• p/p ratio 0.60 +/- 0.04(stat) +/- 0.06(syst) • Central region not yet baryon free
Summary
-19- Rachid Nouicer/UICQCD and HEHI, Moriond, March 2002
Some references• PHOBOS web-site: www.phobos.bnl.gov• Physics Results
• Charged particle multiplicity near mid-rapidity in central Au+Au collisions at 56 and 130 GeV Phys. Rev. Lett. 85, 3100 (2000)
• Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102301 (2001)
• Charged-particle pseudorapidity density distributions from Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102303 (2001)
• Energy dependence of particle multiplicities near mid-rapidity in central Au+Au collisions Phys. Rev. Lett 88, 22302(2002)
• Centrality Dependence of Charged Particle Multiplicity at | in Au+Au Collisions at 130 GeV Phys. Rev. C65, 031901(2002)
• Centrality Dependence of Charged Particle Multiplicity at |<1 in Au+Au Collisions at 130 and 200 GeV Submitted to Phys. Rev. C (2002)
• Technical• Silicon Pad Detectors for the PHOBOS Experiment at RHIC
Nucl. Instr. Meth. A461, 143-149 (2001) • Array of Scintillator Counters for PHOBOS at RHIC
Nucl. Instr. Meth. A474, 38-45 (2001)