# Presentation: 740398

##  Universal Behaviorof Charged Particle Multiplicitiesin Heavy-Ion Collisions

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

##                   Collaboration

- 	_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 Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski,
- 		Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak
- _	__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 Wysłouch
- 	_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

**                  ****Collaboration**

## PHOBOS : Multiplicity & Centrality

**PHOBOS : Multiplicity & Centrality**

- -5.4

- +5.4

**0 keV**

**500**

**Paddle Signal**

**Events**

**(monotonic w/ N****part****)**

**4******** Multiplicity Detector**

## 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 GeV**

**PHOBOS Preliminary**

*N**part*

**Most Central**

## Limiting Fragmentation

- Plotting dN/dvs.
- shows scaling behavior inthe “forward” region

**Limiting Fragmentation**

*** **= ****- y**beam*

**dN/d********/********N****part****/2******

**PHOBOS Au+Au**

**19.6 GeV Preliminary**

*19.6 GeV*

*130 GeV*

*200 GeV*

## Centrality Dependence of dN/d 

**Centrality Dependence of dN/d******** **

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

| ’ ~ -5 | Rises | Saturation?
2-component? |
| --- | --- | --- |
| ’ ~ -1.5 | Stable | Scaling |
| ’~ 1.5 | Falls | Cascading in spectators? |

**Centrality****Dependence**

**Interpretation**

**Location**

## Rapidity Distributions at 200 GeV

**Rapidity Distributions at 200 GeV**

- yT

- 

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

- Correspondence between perturbative and non-perturbative approaches?

**e****+****e****-**** measures dN/dy****T****(rapidity relative to****“thrust” axis)**

**AA/pp ~ 1.4-1.5**

**200 GeV**
**Central Au+Au**

**q**

**q**

## Particle density near midrapidity

**Particle density near midrapidity**

## Total Multiplicity vs. Beam Energy

**Total Multiplicity vs. Beam Energy**

**Central A+A**

## Leading Particle Effect

**Leading Particle Effect**

- Nch

**Basile et al (1980-84)**

**(pp)**

## Approach to Universality

**Approach to Universality**

- p+pp+X :

## How can AA scale like e+e-?

- Above ~3, pion yields constant
- Central AA has ~5-6 *per participant*
- Scaling with Npart
- Reduces leading particle effect
- Scaling with s

****** ****counts**
**# collisions**
**N****part****=********+1**

**pA collisions**

- With increasing 
- Proton “stops” (i.e. deposits energy)
- Pion yield ***saturates***

**E910**

**NA49**

## Centrality Dependence of Nch

**Centrality Dependence of ********N****ch******

**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**

## 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?

- 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?

**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-