Peter Steinberg

Universal Behaviorof Charged Particle Multiplicities

in Heavy-Ion Collisions

Peter SteinbergBrookhaven National Laboratory

for the PHOBOS Collaboration

ICHEP 2002July 24-31, 2002, Amsterdam

Peter Steinberg

Heavy-Ion Collisions

Colliding Nuclei HardCollisions

Parton Cascade

Hadron Gas & Freeze-out

1 2 3 4

• Entropy produced as system evolves• Where does most of it come from?• Initial, partonic or hadronic stage?• Can we understand AA with simpler systems?

VNI Simulations: Geiger, Longacre, Srivastava, nucl-th/9806102

Peter Steinberg

ARGONNE NATIONAL LABORATORYBirger 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, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin 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 Wysłouch

NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang

UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer

UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey,

Marguerite Belt Tonjes

UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

Collaboration

Peter Steinberg

PHOBOS : Centrality & Multiplicity

-5.4 +5.4

0 keV

500

Paddle Signal

Eve

nts

(monotonic w/ Npart)

4 Multiplicity Detector

Participants

Spectators

Spectators

b

Peter Steinberg

PHOBOS Data on dN/d

• Au+Au collisions at s=19.6, 130, 200 GeV• dN/d for ||<5.4 over full azimuth

• Centrality from paddles (130/200) & Nhits (19.6)

• Top 50% of total cross section (Npart~65-360)

dN

/d

19.6 GeV 130 GeV 200 GeVPHOBOS Preliminary

Npart

Most Central

Peter Steinberg

ddN

-2-4 0-6beamy

1

2

3

UA5inelastic

Seen in pp by UA50

53 GeV

200 GeV

546 GeV

900 GeV

Plotting dN/dvs.

shows scaling behavior inthe “forward” region

Limiting Fragmentation

beamy'

= - ybeam

dN

/d

/Np

art/2

19.6 data allowsextrapolation

to extract Nch

PHOBOS Au+Au

19.6 GeV Preliminary

19.6 GeV

130 GeV

200 GeV

Universal limiting distributionseen in both AA and pp

Central 3%

Peter Steinberg

Centrality Dependence of dN/d

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

• Other collision systems?

partpart

Nvsd

dN

N.

2

’ ~ -5 RisesSaturation?

2-component?

’ ~ -1.5 Stable Scaling

’~ 1.5 FallsCascading in spectators?

CentralityDependence InterpretationLocation

200 GeV

130 GeV

19.6 GeV

dN

/d

/Np

art/2

= - ybeam

Peter Steinberg

Rapidity Distributions at 200 GeV

yT

Surprising agreement in shape between AA/e+e- /pp

e+e- measures dN/dyT

(rapidity relative to“thrust” axis)

AA/pp ~ 1.4-1.5

200 GeVCentral Au+Au

q

q

Peter Steinberg

Particle density near midrapidity

e+e- scales likeAA near midrapidity

(dN/dyT )

Peter Steinberg

(Mueller 1983)

)/exp( sAsch BN

pp/pp

A+A

e+e-

Total Multiplicity vs. Beam Energy

Central A+A

Peter Steinberg

Leading Particle EffectNch

effs

Universality

sNsN eeeffpp

Basile et al (1980-84)

(pp)

Subtract energy of leading protons to define effective energy

s

effs 1q

2q

Peter Steinberg

Approach to Universality

Universality

e+e- Au+Au pps s effs

2/sseff

p+pp+X :

Peter Steinberg

How can AA scale like e+e-?

Above ~3, pion yields constantCentral AA has ~5-6 per participant

Scaling with Npart

Reduces leading particle effectScaling with s

counts# collisions

Npart=+1

pA collisions

• With increasing • Proton “stops”

(i.e. deposits energy)• Pion yield saturates

NA49SPS

Relative yield of in pA/pp for y>0

NA49 (unpublished)CERN-SPSLC-P-264-ADD-5

E910NA49

Peter Steinberg

Centrality Dependence of Nch

The Return of the Wounded Nucleon Model…Bialas & Czyz 1976, Elias et al 1978

inel=42 mb(RHIC)

Glauber Monte Carlo

Error band due to high- extrapolation

inel=33 mb (SPS)

inel=21 mb (AGS)

19.6 GeV Preliminary

Au+Au

Peter Steinberg

• Yields in AA scale primarily with Npart

• Even at transverse momentum up to 5 GeV• Gerrit van Nieuwenhuizen’s talk

• New perspective on hadron production?

Two Kinds of Universality

• Universality in the forward region• Data follow “limiting” distribution in

• Universality of total multiplicity• Same for all systems at same s(seff for pp)• “Startling” connection between Au+Au & e+e-

Peter Steinberg

_pp

Au+Au

19.6 GeVpreliminary

130 GeV

200 GeV

Two Component Model:

Charged Particle Production Central Density

Data from PRC 65 061901R (2002)

collpppartpp NxnNnxd

dN )1(

= N

co

ll/(

Np

art/2

)