overview of results from phobos experiment at rhic
DESCRIPTION
Overview of Results from PHOBOS experiment at RHIC. Andrzej Olszewski Institute of Nuclear Physics, Krak ów, Poland for the PHOBOS Collaboration. PHOBOS at RHIC. PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW - PowerPoint PPT PresentationTRANSCRIPT
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -1-
Overview of Resultsfrom PHOBOS experiment at RHIC
Andrzej OlszewskiInstitute of Nuclear Physics, Kraków, Poland
for the
PHOBOS Collaboration
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -2-
PHOBOS at RHIC
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -3-
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, Joel Corbo, Stephen Gushue, Dale Hicks, Burt Holzman,Robert Pak, Marc Rafelski, 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, Michel Rbeiz, 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
Chia Ming Kuo, Willis Lin, Jaw-Luen Tang
Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
Richard Bindel, Alice Mignerey
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -4-
The PHOBOS Detector (2001)
Ring Counters
Time of Flight
Spectrometer
• 4 Multiplicity Array
- Octagon, Vertex & Ring Counters• Mid-rapidity Spectrometer• TOF wall for high-momentum PID• Triggering
- Scintillator Paddles Counters- Zero Degree Calorimeter (ZDC)
Vertex
Octagon
ZDC
z
yx
Paddle Trigger Counter
Cerenkov
137000 silicon pad readout channels
1m
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -5-
Central Part of the Detector
(not to scale)
0.5m
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -6-
PHOBOS in PHOTOS
Octagon Detector
Ring Counter
Silicon pad sizes Octagon Detector: 2.7 x 8.8 mm2
Vertex Detector: 0.5 x (12-24) mm2
Ring Counter: (5x5) - (10x10) mm2
Spectrometer: (1x1) - (0.5x19) mm2
~ 25
cm
Spectrometer
Vertex Detector
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -7-
PHOBOS Running Summary
• Commissioning: (May-July)• Part of silicon installed
• Au+Au collisions at
sNN = 56 GeV and 130 GeV
First published results on dNch/d|||<1, sNN=56 and 130 GeV
• Physics run: (July-August)• 1 spectrometer arm setup
• Au+Au collisions at sNN =
130 GeV: ~3.5 M collisions total
Year 2000 running
Essentially flawless performance of PHOBOS detector
• Commissioning: (mid-July)• Add 2nd spectrometer arm
• Au+Au collisionssNN = 130 GeV and 200 GeV
First published result on dNch/d|||<1, sNN= 200 GeV
• Physics run: (mid-August)• 2 spectrometer arm setup
• Au+Au collisions at sNN =
200 GeV: ~3.5 M collisions by end of August
Year 2001 running
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -8-
Charged particle density
•Versus energyCentral collisions, 0:sNN = 56 and 130 GeV PRL 85 (2000) 3100sNN = 200 GeV, submitted to PRL
•Versus centrality:sNN = 130 GeV, 0 submitted to PRC
•Versus angle and centralitysNN = 130 GeV, ||<5.4 PRL 97 (2001) 102303
Elliptic flow
•Versus angle and centralitysNN= 130 GeV, ||<5.3
QM2001, to be submitted soon
Results to Date
Particle ratios p/p, K-/K+, -/+
Central collisions: sNN = 130 GeV
PRL 97 (2001) 102301
_
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -9-
t (ns)
Eve
nts
Triggering on Collisions
Negative
Paddles
Positive Paddles
ZDC N
ZDC PAu Au
PPPN Paddle Counter
• Coincidence between Paddle counters at t = 0 defines a valid collision
• Paddle + ZDC timing reject background
• Sensitive to 97% of inelastic cross section for Au+Au at sNN = 130/200 GeV
ValidCollision
ZDCCounter
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -10-
Selecting Collision Centrality
Paddle signal (a.u.)
Data
Co
un
ts
Larger signal = more central collision.
Central Collision: Large Npart
Peripheral Collision: Small number of participating nucleons
“side” view of colliding nuclei “side” view of colliding nuclei
3<||<4.5
PN PP
b
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -11-
Multiplicity in Paddles
Np
art
% (Paddle mult.) % (Npart)
HIJING + GEANT
(3<||<4.5)
% Error on Npart
Analysis is limited to events with Npart > 70
Centrality Determination
Npart
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -12-
Charged Particle Density
Measurement
• Energy Dependence • System Size • Angular Dependence
Context
Study
•Energy/entropy density production
•Response to properties of nuclear/partonic medium
•Saturation•Jet quenching
• Importance of hard and soft processes
•Re-scattering effects•Long-range particle correlations
•Memory of the initial geometry in the final state
• Charged Particle Density• Event Anisotropy - Flow
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -13-
Tracklets
• Tracklet: Two-hit combination + vertex position
• >300 tracklets/central event in Vertex, >100 in Spectrometer
Vertexdetector
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -14-
Analog and Digital Hit-Counting
0 +3-3 +5.5-5.5
DigitalCount hits above energy threshold,assume Poisson-statistics in thedistribution of hits among the pads
AnalogUse deposited energy (dE/dx) in each pad to estimate number of particles that crossed the pad
Hits in Octagon, Ring and Vertex
for single event
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -15-
Charged Particle Density
Four counting methods
• Tracking detectors - measurements
• Tracklets in Spectrometer• Tracklets in Vertex detector
• Single layer detectors - 4 measurements
• Use deposited energy (dE/dx) in each Si-pad• Count hits above threshold, assume Poisson-statistics
All four measurements corrected for: secondary particles, feed-down from weak decay, stopping particlesSystematic uncertainty: from 4.5% (Tracklets in Spectrometer) to 10% (Hit counting)
All four methods deliver consistent results - final results averaged
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -16-
Charged Particle Density at 0
PHOBOS first measurements
- charged particle density
- in mid-rapidity- for 6% of the most central events
dNch/d|||<1(56 GeV) = 408 12(stat) 30(syst)
dNch/d|||<1(130 GeV) = 555 12(stat) 35(syst)
dNch/d|||<1(200 GeV) = 650 35(syst)
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -17-
dNch/d|||<1 vs Energy
AGS
PHOBOS 56
RHIC 130
SPS
p+p_
Preliminary
PHOBOS 200
nucl-ex/0108009Submitted to PRL
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -18-
PHOBOS Measurement
90% confidence
dNch/d|||<1: Ratio 200/130 GeV
R200/130 =
1.14 +/- 0.05(sys)
New results for 200 GeV
nucl-ex/0108009
dNch/d|||<1 =
650 35
dNch/d|||<1/0.5Npart
= 3.78 0.25
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -19-
Scaled multiplicity increases
with Npart
Similar to Kharzeev/Nardi
dNch/d = a·Npart + b·Ncoll
Stronger than in EKRT
Less steep than in HIJING
Evolution with Npart
Multiplicity at =0 vs Centrality
sNN =130GeV
nucl-ex/0105011
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -20-
Multiplicity in 4 - Centrality Dependence
The width of the distribution changes with centrality
sNN = 130GeVPRL 97 (2001) 102303
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -21-
3% most central collisions
<Nch> = 4200 470
(dNch/d)/(0.5Npart) central(0-6%)
peripheral(35-45%)
Multiplicity in 4 - Centrality Dependence
central(0-6%)
Total Nch(|| 5.4)
Additional particle
production near =0
PRL 97 (2001) 102303
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -22-
Change in dN/d with Energy
200 GeV - 6%
130 GeV - 6%
UA5 200 GeV(NSD)
•First attempt to compare dN/d shape for Au+Auat 130 and 200 GeV
•‘Limiting fragmentation’ check by plotting dN/d with - Ybeam
•Agreement for AA in thefragmentation region
•Different slope when compared to pp
Systematic errors not shown
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -23-
Azimuthal Angular Distributions
dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R)) + ... )
V2 determines to what extent the initial state spatial/momentum anisotropy is preserved in the final state.
R reaction plane
“head on” view of colliding nuclei
b
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -24-
• Anisotropy increases for peripheral collisions
• Large V2 signal compared to lower energy
Centrality Dependence of V2
V2
Normalized Paddle Signal
SPS
(STAR : Normalized Nch )
|| < 1.0 sNN=130GeV
PHOBOS Systematic error ~ 0.007
Peripheral Collisionsb
Central Collisionsb
17 GeV
Preliminary
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -25-
V2 (elliptical flow) vs
• Averaged over centrality• V2 drops for || > 1.5
V2PHOBOS Preliminary
STAR (PRL)
PHOBOS Systematic error ~ 0.007
sNN= 130 GeV
All Charged
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -26-
• Microscopic viewpoint:
Antiproton/proton ratio determined by: • Baryon stopping;
• Pair production;
• Absorption in nuclear medium
Why Measure Antiparticle/Particle Ratios?
Net
Bary
on
Nu
mb
er
y
• Thermodynamic viewpoint: Particle ratios can be used to estimate hadro-chemical potentials
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -27-
Anti-particle / particle Ratios
p
K+
+
K-
p
-
70 c
m
•Tracking in the spectrometer•Alternate 2T magnetic fields•Energy loss and momentum
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -28-
= 1.00 ±0.01 (stat) ± 0.02 (syst)
K/K+ = 0.91 ± 0.07 (stat) ± 0.06 (syst)
p/p = 0.60 ± 0.04 (stat) ± 0.06 (syst)
K-/K+ vs Energy p/p vs Energy
Results for Ratios
Higher values of K-/K+ and p/p than at lower energies
PRL 97 (2001) 102301
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -29-
Results consistent withB=45±5 MeV, which ismuch lower than that observedat SPS (~240-270 MeV)
Assumes freezeout temp ~170 MeV in statistical model of Redlich (QM01)
Results for RatiosPRL 97 (2001) 102301
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Charged Particle Densities(Entropy)
• dNch/d at 0 per participant• First look at Au+Au at 200 GeV
- increase in density by 14% compared to 130GeV• Logarithmic increase with energy from AGS to RHIC
• Npart evolution stronger then linear, indicates increasing contributions from hard processes
• dNch/d in 4• Additional particle production concentrated
near 0 for central events• Decreasing width with increasing centrality• On average 4200 particles in central collisions at 130GeV
Summary 1
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -31-
Summary 2
• Elliptic flow• Increase of elliptic flow (V2) for more peripherial events
• Increase of flow effect with increasing energy• V2 at mid-rapidity up to 0.06
• V2 drops for || > 1.5
• Particle ratios• K-/K+ and p/p significantly higher than at AGS or SPS
~ 45 MeV vs 270 MeV at SPS• p/p between HIJING and RQMD predictions• Central region closer to baryon free state
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -32-
Outlook: Year 2001
• 100x statistics• Physics:
• low-pT physics
• Spectra• HBT
• Resonances (at low pT
• Event-by-Event physics
• Energy systematics• Species systematics
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The End
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Silicon Signals 200 vs 130 GeV
Signal shapes are (almost) identical:
Methods developed for 130 GeV good also at 200 GeV
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Andrzej Olszewski/INPStrange Quarks in Matter, Frankfurt 2001 -35-
Tracklet counting method (2 Si layers)
Tracklets three-point tracks two-hit combinations+measured event vertex
x ~ 450 my ~ 200 mz ~ 200 m
Spectrometer Vertex Detector
D = (2 + 2) 1/2 < 0.015 || < 0.04 , || < 0.3
The measurements in the two different Si pad detectors(different location, granularity, acceptance, systematics)
dNch/d at mid-rapidity: ||<1
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)N,Z(N
ddN
hitsvtx
Datatrackletsch
(Zvtx, Nhits) = MCprimaries
MCtracklets N/N
TOTAL systematic errors: 4.5% (Spectrometer) 7.5% (Vertex)
FINAL RESULTSCombined Vertex and Spectrometer measurements
(weighted by the inverse of their total systematic error)
Tracklet analysis
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•Count hits in (,Npart) bins
•Evaluate number of particles per hit pad * Assume Poisson statistics P(N)=Ne-/N! - determined by the measured ratio (p) of occupied to empty pads: = ln(1+p) * Perform a multi-Landau fits to E (,Npart) spectra (convoluted with gaussian)
•Calculate acceptance
•Fold in a final background correction (MC) FBkg(,Npart) =(dNch/d)MC
Truth/(dNch/d)MCReconstructedBkg
hit/trhitsch FA
NN
d
dN
Nhits(,Npart)
Ntr/
hit(,Npart)
A(,Zvtx)
FBkg(,Npart)
Hit Counting method
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•Get energy deposited in each Si pad E(,Npart)
•Divide this energy by the average energy per track <E()>
•Correct for the fraction of primaries fprim()
<E> and fprim are obtained from HIJING+GEANT simulations
primch f
EE
d
dN
Hit Counting and Analog methods agree to within 5%(systematic errors in each method are 10%)
Analog method
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• Secondary particles (+2%)• Little material between interaction point and sensitive
volume
• Antiproton absorption in detector (+8%)• From GEANT simulations
• Feed-down from weak decays (-2%)• Reduced by tracking within 10cm of vertex• Further limit by distance-of-closest-approach cut on tracks
Corrections to the Raw Numbers
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