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

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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

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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

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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

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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 :

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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

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• 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

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Centrality Determination

ETot signal distributions Data and MC unbiased

Efficiency distribution for ETot signal

Overall trigger and vertex-finding efficiency is ~ 83 %

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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

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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

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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

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Minimum-Bias dN/d Obtained from the Five Distinct Silicon Centrality Methods

The distributions agree to within 5% PHOBOS DATA

PHOBOS DATA

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Final Minimum-Bias distribution obtained from Silicon Centrality Methods

PHOBOS DATA

• In the following, we will discuss the systematic errors

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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%

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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

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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

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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

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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

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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

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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

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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 !