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Rachid Nouicer 1
University of Illinois at Chicago and
Brookhaven National Laboratory
for the Collaboration
Seminar at BNL November 14, 2003
The Latest Results from PHOBOS @ RHIC
Pseudorapidity Distribution of Charged Particles
in d + Au Collisions at 200 GeV
NNS
Rachid NOUICER
Rachid Nouicer 2
68 Participants; 8 Institutions; 3 Countries
PHOBOS Collaboration (October 2003)
Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley,
Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski,
Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue,
Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson, David Hofman, Richard
Hollis,
Roman Hołyński, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Nazim Khan, Piotr
Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen,
Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed,
Michael Ricci,
Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd Smith,
Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek,
Carla Vale, Siarhei Vaurynovich, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs,
Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
Rachid Nouicer 3
Outline
• PHOBOS multiplicity detector
• Centrality determination and cross checks
• Minimum-bias pseudorapidity distribution
• Systematic errors
• Comparison of d + Au to Au + Au and p + p systems
• Comparison to the predictions of parton saturation model and microscopic models (HIJING, RQMD, AMPT)
• Summary
Rachid Nouicer 4
PHOBOS Multiplicity Detector
1m Triggering “Scintillatorcounter arrays”
ZDC
ZDC
Ring Counters
Octagon
• 4Multiplicity Array: - Central Octagon Barrel : - 6 Rings at higher Pseudorapidity : • Triggering: Scintillator counter arrays
5.4|η| 3.0 3.2|η|
Sample Silicon pad sizesOctagon Detector: 2.7 x 8.8 mm2
Ring Counter: 20 –105 mm2
Rachid Nouicer 5
PHOBOS Capability in Charged Particle Multiplicity Analysis
Event display of One collision event
Octagon region Rings Rings
5.4η 5.4-
• Two analysis methods :
1- Hit-Counting Analysis based on ratio of hit pads to empty pads using Poisson statistics 2- Analog Analysis based on particle energy deposited in each pad
Rachid Nouicer 6
Extensive systematic Au + Au data d
N/d
19.6 GeV 130 GeV 200 GeVPHOBOS PHOBOS PHOBOS
Typical systematic band (90%C.L.)
Phys. Rev. Lett., 91, 052303 (2003)
• Phys. Rev. Lett. 85, 3100 (2000)• Phys. Rev. Lett. 87, 102303 (2001)• Phys. Rev. C 65 , 31901R (2002)• Phys. Rev. Lett. 88 , 22302 (2002)• Phys. Rev. C 65 , 061901R (2002) • Phys. Rev. Lett. 91, 052303 (2003)• nucl-ex/0301017, subm. to PRL • nucl-ex/0311009, subm. to PRL
PHOBOS Multiplicity papers :
Rachid Nouicer 7
Parton Saturation Describes Au + Au
Kharzeev & Levin, Phys. Lett. B523 (2001) 79
Au + Au at 130 GeV
• We need a simpler system such as d + Au in order to understand a complex system Au + Au • The results of d+Au are crucial for testing the saturation approach
Rachid Nouicer 8
• The goal is to measure minimum-bias dNch/d
• Challenge is to correct for trigger and event selection bias
• Measure the dNch/din narrow bins of centrality and integrate over centrality to produce a minimum-bias result
• Cross check influence of auto-correlations
PHOBOS Capability in Charged Particle Multiplicity Analysis
Rachid Nouicer 9
Centrality Determination
ETot signal distributions Data and MC unbiased
Efficiency distribution for ETot signal
Overall trigger and vertex-finding efficiency is ~ 83 %
Rachid Nouicer 10
Centrality Determination
DATA measured cross section
MC distribution with trigger and vertex bias
- Data and MC (biased) distributions match well
- Data cut = MC cut X scale factor
Normalize
Scale
Comparison of the signal distributions from Data and MC (HIJING)
Scaling factor =1.046
Details of centrality determination were presented in DNP talks: A. Iordanova and R. Hollis at UIC
Rachid Nouicer 11
Centrality Determination
- Unbiased ETot signal distribution represents the full geometrical cross section
- Slice this distribution into percentile bins
- For each slice we extract dN/d
0.78.1partN
HIJING
• Number of participants for minimum-bias is
Rachid Nouicer 12
Five Distinct Silicon Centrality Methods for Cross Checks
1) ETot method | | < 5.4
2) EOct method | | < 3
3) EAuDir method < -3
4) EdDir method > 3
5) ERing method 3 <| < 5.4
ETot
EOct
EAuDir
EdDirERing
Centrality methods
Rachid Nouicer 13
Minimum-Bias dN/d Obtained from the Five Distinct Silicon Centrality Methods
The distributions agree to within 5% PHOBOS DATA
PHOBOS DATA
Rachid Nouicer 14
Final Minimum-Bias distribution obtained from Silicon Centrality Methods
PHOBOS DATA
• In the following, we will discuss the systematic errors
Rachid Nouicer 15
Systematic Errors
• Analysis methods : Digital and Analog methods : 1-5%
• Silicon centrality methods : 1-5%
• HIJING/ feed-down corrections: 5-18%
• Efficiency from a different Monte-Carlo simulation : 5%
These systematic errors are dependent and the major contributions are :
At the total systematic error is ~ 7%
Rachid Nouicer 16
Final Minimum-Bias Pseudorapidity Distribution in d + Au at 200 GeV
0.7(syst)9.4 0.6|η|dη
dN
• Charged particle pseudorapidity density near midrapidity is
• Integrated primary charged particle multiplicity in the measured region is
6(syst)82 ch5.4|η|N
nucl-ex/0311009 and Submitted to PRL
PHOBOS DATA
Rachid Nouicer 17
Estimates of the Total Charged Particle Production
Using Triple Gaussian fit
• Missing charged particle multiplicity is
5 chmissN
Using AMPT Model
• Upper limit including systematic errors : 110 ch
totN
• Estimated total charged particle multiplicity is
2307-87 ch
totN
Rachid Nouicer 18
Comparison of d + Au to Au + Au and p + p Systems at the Same Energy
nucl-ex/0311009 and Submitted to PRL
• Normalized to the number of participants / 2
• Compared to p + p collisions:
• increase in particle production in the gold direction
• reduction of particle production in the deuteron direction
• The total integrated charged particle multiplicity normalized to the number of participant in d + Au and p + p is approximately the same:
.5 10 212
1 /Npart chN : pp
0.8.7 10 /Npart chN :dAu
PHOBOS DATA d + Au and Au + Au
Rachid Nouicer 19
Comparison to Parton Saturation and RQMD Models
• Parton saturation (KLN) and RQMD models are inconsistent with the data
• KLN model overestimates the height of the gold side peak, underestimates its width, and predicts the peak at ~ -3 rather than = -1.9 as in data.
nucl-ex/0311009 and Submitted to PRL
Parton saturation model predictions for d + Au: D. Kharzeev et al., arXiv:hep-ph/0212316
Rachid Nouicer 20
nucl-ex/0311009 and submitted to PRL
Comparison to AMPT and HIJING Models
• The HIJING calculation
• reproduces the deuteron side and the peak of the gold-side
• fails to reproduce the tail in the gold direction ( < -2.5).
• AMPT predictions
• With & without final-state interactions fall close to the data.
• FSI appear to broaden the gold-side peak, leading to moderate increase of the particle multiplicity in the region < -3.5.
AMPT predictions for d + Au : Zi-Wei Lin et al., arXiv:nucl-ph/0301025
Rachid Nouicer 21
Ratio of the Model predictions to data
nucl-ex/0311009 and submitted to PRL
• Quantitative evaluation of the model predictions, expressed as the ratio of the model prediction to the data
Rachid Nouicer 22
Summary
• The dN/d in d + Au collisions at 200 GeV has been measured
• The distribution is broader than pp and peaked in the gold direction
• The average pseudorapidity density is
• The measured integrated charged particle multiplicity is
• The total integrated charged particle multiplicity normalized to the
number of participant in d + Au and p + p is approximately the same
• Comparison to the predictions of microscopic models is made
• The data disfavors the predictions of parton saturation model
0.7(syst)9.4
6(syst)82
• The latest news from PHOBOS: More to come !