# Presentation: 383278

## Centrality Dependence of Charged Hadron Production at RHICd+Au vs Au+Au

- Gunther Roland/MIT
- for the
- PHOBOS Collaboration

**BNL June 18, 2003**

##                   Collaboration

- Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,
- Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll,
- Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen,
- Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson,
- David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson,
- Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven Manly,
- Alice Mignerey, Gerrit van Nieuwenhuizen, Aaron Noell, Rachid Nouicer, Andrzej Olszewski,
- Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland,
- Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski,
- Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng,
- Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard Wadsworth, Frank Wolfs,  Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang
- 	ARGONNE NATIONAL LABORATORY	BROOKHAVEN NATIONAL LABORATORY
- 	INSTITUTE OF NUCLEAR PHYSICS, KRAKOW	MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- 	NATIONAL CENTRAL UNIVERSITY, TAIWAN	UNIVERSITY OF ILLINOIS AT CHICAGO
- 	UNIVERSITY OF MARYLAND	UNIVERSITY OF ROCHESTER

## ?

***How to connect observed***
***final state particles to ***
***theory of strong interaction?***

**?**

## Particle Multiplicity at RHIC

**Rapidity Density**

**600**

**  ****1200**

**Compilation by K. Eskola**

**Particle Multiplicity at RHIC**

## Particle Multiplicity at RHIC

**PHOBOS multiplicity papers:**
**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) **
**nucl-ex/0210015, PRL in Press**
**nucl-ex/0301017, subm. to PRL****  ****  **

***Multiplicity at low end of range***
***But: Energy density 30x nuclear matter***
***Most models didn’t do so well***

## Parton Saturation

**Parton Saturation**

***Low Energy***

***High Energy***

**Particle Multiplicity at RHIC**

**Color Glass**

## Particle Multiplicity at RHIC

**Color Glass**

**Hadron multiplicities at RHIC well **
**described by Parton Saturation**

**Particle Multiplicity at RHIC**

**Kharzeev & Levin, Phys. Lett. B523 (2001) 79**

**Data: PHOBOS,**
**Phys. Rev. Lett. 87, 102303 (2001)**

## pT Spectra for Au+Au @ 200 GeV

## Centrality Dependence vs pT

**PHOBOS, nucl-ex/0302015**

***Similar centrality dependence at***
***p******T****** = 0.5 and 4 GeV/c !***

## Predictions for  d+Au

**Vitev, nucl-th/0302002, Phys.Lett.B in press **
**Vitev and M.Gyulassy, Phys.Rev.Lett. 89 (2002)**

** ****Central**

**Peripheral**

**Kharzeev, Levin, McLerran, hep-ph/021332**

***“******~30%suppression of high p******T****** particles”***
**(central vs peripheral)**

**16% increase central vs peripheral**

***Nuclear Modification Factor R******dAu***

**Parton Saturation**

**pQCD**

## PHOBOS Detector 2003

**PHOBOS Detector 2003**

- SPECTRIG

- mini-pCal

- pCal

**Moved TOF walls back **
**5 m from interaction point**
**New on-line high p****T  ****Spectrometer Trigger**
**New “time-zero” (T0) Cerenkov detectors  **
**On-line vertexing and ToF start time**
**Forward proton calorimeters on Gold and Deuteron sides**
**DAQ upgrade (x10)**

## Centrality Determination in d+Au

**Centrality Determination in d+Au**

**Multiplicity distribution**

**Pseudorapidity**

_**Glauber Calculation**_
**Hijing 1.383**
**Hulthen w.f.**
**41mb inelastic cross-section**
**Full GEANT Simulation**

**HIJING Simulation**

**dN/d******

**Counts**

## d+Au pT Spectra

**d+Au p****T**** Spectra**

**PHOBOS d+Au: nucl-ex/0306025**

## RdAu vs pT

- central Au+Au

**All syst. uncertainties: 90% C.L.**

**PHOBOS d+Au: nucl-ex/0306025**

**R****dAu**** vs p****T**

## Centrality dependence of RdAu

**Data disfavor initial state **
**interpretation of Au+Au **
**high-p****T**** suppression**

**N.B. Smaller ********pp****inel  ****would increase **
**R****dAu**** central vs R****dAu**** peripheral**

**PHOBOS d+Au: nucl-ex/0306025**

**All syst. uncertainties: 90% C.L.**

## Connection to QCD

**Initial State**

**‘****Final State’ Interactions**

**Multiplicity systematics**
**connected to initial state**
**Consistent with parton **
**saturation picture**

**Interaction of fast partons**
**with dense medium has **
**been observed**
**Quantitative diagnostic **
**tool now established**

**Connection to QCD**