P1253296552GxfuF

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Global Observables from AuAu, CuCu, dAu and
pp Collisions at RHIC Energies
Rachid NOUICER Brookhaven National Laboratory
(BNL)
(for PHOBOS Collaboration)
PANIC05 Particles and Nuclei International
Conference Santa Fe, NM - October 24-28, 2005
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PHOBOS Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Zhengwei Chai,
Vasundhara Chetluru, Edmundo García, Tomasz
Gburek, Kristjan Gulbrandsen, Clive Halliwell,
Joshua Hamblen, Ian Harnarine, Conor Henderson,
David Hofman, Richard Hollis, Roman Holynski,
Burt Holzman, Aneta Iordanova, Jay Kane,Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Constantin Loizides, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Corey
Reed, Eric Richardson, Christof Roland, Gunther
Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George
Stephans, Andrei Sukhanov, Artur Szostak,
Marguerite Belt Tonjes, Adam Trzupek, Sergei
Vaurynovich, Robin Verdier, Gábor Veres, Peter
Walters, Edward Wenger, Donald Willhelm, Frank
Wolfs, Barbara Wosiek, Krzysztof Wozniak, Shaun
Wyngaardt, Bolek Wyslouch ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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Outline
What can we learn from AuAu and CuCu
Collisions at
RHIC Energies?

• What can we learn from charged hadron
  production in CuCu compared to AuAu?
• What is the interplay between collision
  centrality (geometry) and collision
  energy?
• How does elliptic flow scale with geometry and
  density? (See Alice Mignereys Talk session
  4, Section I.7).
• Summary

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Pseudorapidity Distributions of Charged Particles
New Results from PHOBOS CuCu at 62.4 and 200 GeV
There is no evidence for two separate regions
mid-rapidity and fragmentation regions in any
of the RHIC energies Continuous distributions
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Pseudorapidity Distributions of Charged Particles
We define the mid-rapidity region h lt 1

• PHOBOS references for the data
• AuAu PRL 91, 052303 (2003)
  PRC nucl-ex/0509034
• dAu PRL 93, 082301 (2004)
• CuCu QM2005 e-Print nucl-ex/0510042

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Particle Density at Mid-rapidity h lt 1
Interplay Between Collision Energy and System Size
AuAu PRL 91, 052303 (2003)
PRC nucl-ex/0509034
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Particle Density at Mid-rapidity h lt 1
Interplay Between Collision Energy and System
Size
AuAu, PbPb, CuCu and p(p) p Collisions
AuAu PRL 91, 052303 (2003)
PRC nucl-ex/0509034 CuCu QM2005 e-Print
nucl-ex/0510042
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Particle Density at Mid-rapidity h lt 1
Interplay Between Collision Energy and System Size
AuAu, PbPb, CuCu and p(p) p Collisions
In symmetric collisions Nucleus-Nucleus it
seems the density per nucleon doesnt depend on
the size of the two colliding nuclei but it
depends on the colliding energy
AuAu PRL 91, 052303 (2003)
PRC nucl-ex/0509034 CuCu QM2005 e-Print
nucl-ex/0510042
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Similarity Between CuCu vs AuAu Collisions
dN/d? in CuCu vs AuAu Collisions at Similar
Npart
200 GeV
62.4 GeV
CuCu Preliminary 3-6, Npart 100
CuCu Preliminary 3-6, Npart 96
AuAu 35-40, Npart 99
AuAu 35-40,Npart 98
Unscaled dN/d? very similar for AuAu and CuCu
at same Npart
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Similarity Between CuCu vs AuAu Collisions
dN/d? in CuCu vs AuAu Collisions at Similar
Npart
This is not coincidence
62.4 GeV
200 GeV
CuCu Preliminary 15-25, Npart 61
CuCu Preliminary 15-25, Npart 60
AuAu 45-55, Npart 56
AuAu 45-50,Npart 62
For same system size (Npart ), CuCu and AuAu
are very similar.
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Charged Particle Production in Forward Regions
Extended Longitudinal Scaling Limiting
Fragmentation Scenario
AuAu/CuCu Collisions
In the rest frame of one of the colliding nuclei
Extended longitudinal scaling appears to be
independent of energy and size of the colliding
nuclei for more central collision over a very
large range of ?-ybeam
Centrality 0-6
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Charged Hadron pT Spectra (Rapidity Range 0.2 lt
y lt1.4)
62.4 GeV
200 GeV
AuAu
preliminary
preliminary
CuCu
dAu

• PHOBOS references for the data
• AuAu PRL 94, 082304 (2005),
• PLB 578, 297 (2004)
• dAu Phys. Rev. Lett 91, 072302 (2003)
• CuCu QM2005 e-Print nucl-ex/0510042

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Similarity Between CuCu vs AuAu Collisions
Nuclear Modification Factor vs Npart
200 GeV
AuAu PRL 94, 082304 (2005), PLB 578, 297 (2004)
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Similarity Between CuCu vs AuAu Collisions
Nuclear Modification Factor vs Npart
200 GeV
AuAu PRL 94, 082304 (2005), PLB 578, 297 (2004)
CuCu G. Roland Talk QM2005, e-Print
nucl-ex/0510042
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Similarity Between CuCu vs AuAu Collisions
Nuclear Modification Factor vs Npart
62.4 GeV
CuCu G. Roland Talk QM2005, e-Print
nucl-ex/0510042
AuAu PRL 94, 082304 (2005)
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Similarity Between CuCu vs AuAu Collisions
Anti-proton/proton Ratio
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Factorization
What is the interplay between collision
centrality (geometry) and collision energy?
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Interplay Between Collision Centrality (Geometry)
and Collision Energy
Factorization of Particle Density at Mid-rapidity
(hlt1)
PHOBOS
AuAu
CuCu preliminary
We observe Energy/Centrality Factorization. Is
this factorization an initial state effect?
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Interplay Between Collision Centrality (Geometry)
and Collision Energy
Factorization in pT at Mid-rapidity
Ratio of charged hadron yields in 200 GeV to 62
GeV
ltpTgt 0.25 GeV/c
ltpTgt 1.25 GeV/c
ltpTgt 2.5 GeV/c
ltpTgt 3.88 GeV/c
ltpTgt 3.38 GeV/c
Energy/Centrality factorization up to pT 4
GeV/c for Npart gt 40
AuAu PRL 94, 082304 (2005)
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System Size Independence of Pseudorapidity Shapes
Factorization of dN/dh Shapes
Systematic errors are not shown
AuAu at 200 GeV
CuCu at 200 GeV
dNFact.(CuCu x) dNMeas.(CuCu x)
Does this factorization work and can we predict
the dN/dh distributions of CuCu based on AuAu?
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System Size Independence of Pseudorapidity Shapes
Factorization of dN/dh Shapes
200 GeV
It thus appears that dN/dh shapes are independent
of the overall size of the colliding nuclei, at
least between the CuCu and AuAu systems studied
here.
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Summary I
Scaling of Hadron Production
What we can learn from charged hadron production
in CuCu compared to AuAu?

• For the same system size (Npart, Ncoll) and at
  the same energy,
• CuCu and AuAu are very similar
• Particle Density
• Extended Longitudinal Scaling
• Total Multiplicity
• Particle Ratio p/p
• Nuclear Modification dN/dpT (RAA)

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Summary II
Geometry and Energy
What is the interplay between collision
centrality (geometry) and collision energy?

• Factorization of geometry and energy dependence
  is observed
• Particle Density at Mid-rapidity (hlt1)
• pT spectra
• dN/dh Shapes

Do these Scaling and Factorization observations
in charged particle production persist to HIC
at LHC?