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Results from the PHOBOS experiment at RHIC. Birger Back Argonne National Laboratory for the PHOBOS Collaboration. PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY - PowerPoint PPT Presentation
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Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Results from the PHOBOS experiment at RHIC
Birger Back Argonne National Laboratory
for the PHOBOS Collaboration
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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PHOBOS Collaboration
ARGONNE NATIONAL LABORATORY
BROOKHAVEN NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF ROCHESTER
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND
Birger Back, Nigel George, Alan Wuosmaa
Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg,Andrei Sukhanov
Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski,Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek,Barbara Wosiek, Krzysztof Wozniak
Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed,Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin,Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen,Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch
Willis Lin, Jaw-Luen Tang
Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
Russell Betts, Clive Halliwell, David Hofman, Burt Holzman,Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter
Richard Bindel, Edmundo Garcia, Alice Mignerey
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Outline
• Apparatus• 2000 run statistics• Physics results
• Charged particle multiplicity • Energy dependence at h=0 • Centrality dependence at h=0 • Pseudo-rapidity distributions • Total charged particle multiplicity
• Flow of charged particles• Antiparticle / particle ratios
• Summary• 2001 run plan • Future upgrade plans
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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PHOBOS Detector
Ring Counters
Paddle Trigger Counter
Spectrometer
TOF
Octagon+Vertex
• 96000 Silicon Pad channels
• 4 Multiplicity Array • Mid-rapidity Spectrometer• Scintillator Paddles + Zero Degree Calorimeter for triggering• TOF wall for high-momentum PID
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Year 2000 running
• Commissioning run: (May-July)• Sacrificial detectors installed• 56 GeV: 6352 collisions• 130 GeV: 12074 collisions
• Physics run: (July-August)• Full complement of detectors• 130 GeV: ~3.5 M collisions
• Well over 1 TB of data written to tape
• Essentially flawless performance of PHOBOS detector
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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• Energy Dependence (vs. AGS/SPS Data)
• System Size (p+p, Npart Dependence )
Results from 2000 run
MEASUREMENT Charged Particle DensityEvent Anisotropy - FlowParticle Ratios
CONTEXT
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Selecting Collisions
• Coincidence between Paddle counters• Paddle + ZDC timing reject background
• Sensitive to 97% of inelastic cross-section for Au+Au at SsNN = 130 GeV
Negative
Paddles
Positive Paddles
ZDC N
ZDC PAu Au
x
z
PPPN
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Multiplicity of charged particles
• Physics motivation• Time integral of particle production during the collision• Total entropy production
• Lots of existing data for pp, pA, AB,AA• How do RHIC data fit into this picture?
• Methods of analysis• 2 Si layers: Tracklet counting• 1 Si layer: Hit counting – Poisson statistics• Check with energy deposition
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Multiplicity from tracklet counting• Select 6% most central events
• Count Tracklets near = 0Commissioning runMay-July 2000
Ss = 56 and 130 GeV
Spectrometer
Vertex
Double Si layer
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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First RHIC physics result: Back et al., PRL 85 (2000) 3100About 20 theoretical papers (Feb 15, 2001)
Multiplicity at =0 vs Energy
RESULTSs dN/dh56 GeV 4081230130 GeV 5551235
Ss 2dN/dh/Npart
56 GeV 2.47.10.25130 GeV 3.24.10.25
Ratio: 1.31.04.05
@ 130 GeV 30% higher than p+p70% higher than SPS
SPS
Phobos
p+p
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Some model comparisons
HIJING EKRT (saturation model)
• 40% increase from p+p to central Au+Au• Data constrain model parameter space• Further insight from centrality dependence
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Multiplicity at =0 vs Centrality (130 GeV)
Physics run July-Sept 2000
Complete year 1 setup
Tracklets in spectrometerand vertex
12 centrality bins for upper55% of cross section
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Multiplicity at =0 vs Npart
Npart
•Good agreement with previous PHOBOS point•Good agreement with recent PHENIX data•Neither HIJING nor EKRT describe data well
Yellow band: Systematic uncertainty
PreliminarydN
ch/d/
(0.5
*Npa
rt)
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Multiplicity in 4(Hit counting)
• Determine dNch/d for –5.4 < < 5.4
• Shape• Total multiplicity
• Evolution vs Npart
• Hit counting
Octagon
Rings
Single Si layer
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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PHOBOS Multiplicity detectors
Octagon 1 of 6 Rings
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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1 Count hits binned in , centrality (b)
2 Calculate acceptance A(ZVTX) for that event
3 Find occupancy in hit pads O(,b) by counting empty to hit channels assuming Poisson statistics
4 Fold in a background correction factor fB(,b)
dNch
d =hits
O(,b) ×fB(,b)
A(ZVTX)
E depositionin multiplicitydetectors for one event.
Rings Octagon Rings
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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dNch/d vs Centrality Preliminary
Statistical errors only - 10-20% systematical uncertainty
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Centrality dependence of dN/dh
Phobos HIJING
Central
•Increased particle production at mid-rapidity•Differences in shapes
Mid central
Peripheral
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Centrality Dependence of Nch(||<5.4)
Npart
PHOBOS Prelim.
±10% Systematic Uncertainty±10% Systematic Uncertainty
HIJING
Nch
(||
<5.
4)
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Elliptic Flow
dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )
b (reaction plane)
Octagon Ring
|| < 1.0
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Hydrodynamic modelV2
Normalized Paddle Signal
Systematic error ~ 0.007
|| < 1.0
SPS
AGS
Preliminary
Large V2 signal compared to lower energy
Preliminary
Centrality Dependence
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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V2 PHOBOS STAR (PRL)
Elliptical flow vs
• Averaged over centrality
• V2 drops for || > 1.5
Preliminary
Systematic error ~ 0.007
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Anti-particle / particle ratios
•Tracking in the spectrometer•Alternate 2T magnetic fields•Energy loss and momentum
+p
K+
+
K-
p
-
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Particle Ratios
Central region not baryon-free
Preliminary
.)syst(..)stat(..
.)syst(..)stat(..
.)syst(..)stat(..
p
p
K
K
10050540
10090910
050010011
Centrality =12 %<Npart> ~ 310
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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• dNch/d @=0 per participant• 70% higher than SPS for central Au+Au• 40% higher than p+p at RHIC energy• Npart evolution between HIJING and EKRT
• dNch/d in 4• <Nch> = 4100 +/- 410 (||< 5.4) for 3% central• Additional particle production near =0 for central events• Wider than HIJING
• Elliptic flow• V2 up to 0.06 – close to hydrodynamic limit• larger than SPS• V2 drops for || > 1.5
• Particle ratios• p/p ratio 0.54 +/- 0.1 • between HIJING and RQMD• Central region not yet baryon free – maybe at 200 GeV
Summary
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Outlook I: 2001
• 100x statistics• Both arms completed• Physics:
• low-pT physics
• Spectra• HBT
• Resonances (at low pT
• Event-by-Event physics
• Energy systematics• Species systematics
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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Outlook II: 2003 + beyond
Micro-Vertex
Transition Radiation Detector
EM-Calorimeter
• Existing Spectrometer• High rate (> 0.5 kHz)• High Resolution
• Add
• Micro-vertex Detector• Narrow beam-pipe• ALICE prototype TRD
Electron ID• EM-Calorimeter
•Charm Production at RHIC•Measure single electrons from displaced vertices
Birger Back/ANLWinter Workshop on Nuclear Dynamics, 2001
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The End