Universal Behavior of Charged Particle Multiplicities in HeavyIon Collisions

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Universal Behaviorof Charged Particle
Multiplicitiesin Heavy-Ion Collisions

• Peter Steinberg
• Brookhaven National Laboratory
• for the PHOBOS Collaboration
• Quark Matter 2002
• July 18-24, 2002, Nantes

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Collaboration
ARGONNE NATIONAL LABORATORY Birger Back, Alan
Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark
Baker, Donald Barton, Alan Carroll, Nigel George,
Stephen Gushue, George Heintzelman, Burt
Holzman, Robert Pak, Louis Remsberg, Peter
Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR
PHYSICS, KRAKOW Andrzej Budzanowski, Roman
Holynski, Jerzy Michalowski, Andrzej Olszewski,
Pawel Sawicki, Marek Stodulski, Adam Trzupek,
Barbara Wosiek, Krzysztof Wozniak MASSACHUSETTS
INSTITUTE OF TECHNOLOGY Maartin Ballintijn, Wit
Busza (Spokesperson), Patrick Decowski, Kristjan
Gulbrandsen, Conor Henderson, Jay Kane, Judith
Katzy, Piotr Kulinich, Jang Woo Lee, Heinz
Pernegger, Corey Reed, Christof Roland, Gunther
Roland, Leslie Rosenberg, Pradeep Sarin,
Stephen Steadman, George Stephans, Carla Vale,
Gerrit van Nieuwenhuizen, Gábor Veres, Robin
Verdier, Bernard Wadsworth, Bolek
Wyslouch NATIONAL CENTRAL UNIVERSITY,
TAIWAN Chia Ming Kuo, Willis Lin, Jaw-Luen
Tang UNIVERSITY OF ILLINOIS AT CHICAGO Russell
Betts, Edmundo Garcia, Clive Halliwell, David
Hofman, Richard Hollis, Aneta Iordanova, Wojtek
Kucewicz, Don McLeod, Rachid Nouicer, Michael
Reuter, Joe Sagerer UNIVERSITY OF
MARYLAND Abigail Bickley, Richard Bindel, Alice
Mignerey, Marguerite Belt Tonjes UNIVERSITY
OF ROCHESTER Joshua Hamblen, Erik Johnson, Nazim
Khan, Steven Manly, Inkyu Park, Wojtek
Skulski, Ray Teng, Frank Wolfs
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PHOBOS Multiplicity Centrality
Events
Paddle Signal
(monotonic w/ Npart)
4p Multiplicity Detector
500
0 keV
5.4
-5.4
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PHOBOS Data on dN/dh
130 GeV
200 GeV
19.6 GeV
PHOBOS Preliminary
dN/dh
Most Central
Npart
h
h
h

• AuAu collisions at ?s19.6, 130, 200 GeV
• dN/dh for hlt5.4 over full azimuth
• Centrality from paddles (130/200) Nhits (19.6)
• Top 50 of total cross section (Npart65-360)

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Limiting Fragmentation
Plotting dN/dh vs. shows scaling behavior
inthe forward region?
PHOBOS AuAu
200 GeV
19.6 GeV Preliminary
130 GeV
dN/dh?/?Npart/2?
19.6 GeV
h? h - ybeam
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Centrality Dependence of dN/dh?
CentralityDependence
Interpretation
Location

• Are these effects related?
• Long-range correlations?
• Energy conservation?
• Stopping?
• Other collision systems?

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Rapidity Distributions at 200 GeV
q
q
200 GeV Central AuAu
ee- measures dN/dyT(rapidity relative
tothrust axis)
yT
h
AA/pp 1.4-1.5
Surprising agreement in shape between AA/ee- /pp
Correspondence between perturbative and
non-perturbative approaches?
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Particle density near midrapidity
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Total Multiplicity vs. Beam Energy
Central AA
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Leading Particle Effect
?Nch?
(pp)
Basile et al (1980-84)
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Approach to Universality
pp?pX
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How can AA scale like ee-?
E910
pA collisions
NA49
n counts collisions Npartn1

• With increasing n
• Proton stops (i.e. deposits energy)
• Pion yield saturates

• Above n3, pion yields constant
• Central AA has n5-6 per participant
• Scaling with Npart
• Reduces leading particle effect
• Scaling with ?s

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Centrality Dependence of ?Nch?
Error band due to high-h extrapolation
sinel42 mb (RHIC)
AuAu
sinel33 mb (SPS)
sinel21 mb (AGS)
Glauber Monte Carlo
19.6 GeV Preliminary
The Return of the Wounded Nucleon Model
Bialas Czyz 1976, Elias et al 1978
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Two Kinds of Universality

• Universality in the forward region
• Data follow limiting distribution in h?
• Universality of total multiplicity
• Same for all systems at same ?s(?seff for pp)
• Startling connection between AuAu ee-

• Total yields in AA scale primarily with Npart
• For additional discussion of Npart scaling
• M. Baker Results from PHOBOS Friday 10h00
• C. Roland Particle Spectra Saturday 14h30
  parallel
• New perspective on particle production?