# Presentation: 228508

## Global Observations from PHOBOSA story of scaling 

- Mark D. Baker
*Brookhaven National Laboratory** *
- for the                   Collaboration
***8th International Wigner Symposium***
***May 28, 2003***

- Mark D. Baker

##                   Collaboration (May 2003)

- 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

- Mark D. Baker

## PHOBOS Detector in 2002

**1m**

**ZDC**

**ZDC**

**12m Be Beampipe**

**ZDC**

**ZDC**

- Mark D. Baker

## Extensive systematic data set

**dN/d******

****

****

****

**19.6 GeV**

**130 GeV**

**200 GeV**

-  d2N/dd over 11 x 2 units of x 
-  Au+Au at s=19.6, (56), 130, & 200 GeV
-  p+p and d+Au on the way

**PHOBOS**

**PHOBOS**

**PHOBOS**

**Typical systematic band ****                               (90%C.L.)**

****

****

**Phys. Rev. Lett. (2003), in press,  arXiv:nucl-ex/0210015**

- Mark D. Baker

## Scaling of rare (hard) processes

**L~A****1/3**

**A**

**N****coll****    = ****# of NN collisions ****~A****4/3    ****(formally Glauber T****AA****(b))**
**N****part****/2**** ****=****  # of participating ****nucleons****: ****A**

- Mark D. Baker

## Midrapidity charged particle production

**|********|<1**

- Collision scaling does NOT disappear at low energy.
- Problem for naïve “minijet” based models.

- Au+Au

**200 GeV**

**130 GeV**

- Preliminary 19.6 GeV

- Mark D. Baker

## Initial state parton saturation? 

- Initial state parton saturation?

**QM2002: nucl-ex/0212009**

******~0.25 from fits to HERA data: **
**                      ****xG(x)~x******
**Describes energy dependence correctly!**

- Kharzeev, Levin, Nardi,
- hep-ph/0111315

**200 GeV**

**130 GeV**

- Preliminary 19.6 GeV

- Mark D. Baker

## Parton Saturation describes AA

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

- PRL 87 (2001)

**Same********From HERA******
**describes dN/d******** shape correctly!**
**(& energy & centrality dep.)**

- Mark D. Baker

## Energy Dependence of Central dN/d

**Scale by N****part****/2 & shift to ********=********- y****beam**

**The “fragmentation region” extent grows with ********s****NN**

**Systematic errors not shown**

**PHOBOS Au+Au**

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>**

**dN****ch****/d******

**6% central**

**Phys. Rev. Lett. (2003), in press,  arXiv:nucl-ex/0210015**

- Mark D. Baker

## “xF scaling” in AuAu

**p + p inel.**** **** **

- UA5, Z.Phys.C33, 1 (1986)

**dN/d******

**Systematic errors not shown**

**19.6 GeV is preliminary**

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>**

- 6% central

- “xF scaling” in AuAu

- Mark D. Baker

## Nch scales with Npart 

- Nch scales with Npart

**Error bands due to **
**high-******** extrapolation**

**Au+Au**

**(preliminary)**

**Total charged particle production ~ N****part**

**e+e-**

**e+e-**

**e+e-**

-  nucl-ex/0301017

- Mark D. Baker

## AA and e+e- similar in shape as well as magnitude

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

- AA and e+e- similar in shape as well as magnitude

**200 GeV**

- Mark D. Baker

## Comparison of Nch vs. Energy

- Comparison of Nch vs. Energy

- pQCD e+e- Calculation

-  nucl-ex/0301017; Submitted for Publication

-  nucl-ex/0301017

- Mark D. Baker

## Comparison of Nch vs. Energy

- Comparison of Nch vs. Energy

**Different systems converge **
**at high energy.**

**PHOBOS Preliminary **
**          ****Central Au+Au**

**Central****       AA**

**pp (pp) data @ ********s****eff**

**e****+****e****-**

**1             10           10****2****          10****3**** **

******s (GeV)**

- Universality?

-  nucl-ex/0301017

- Mark D. Baker

## PT Distribution of Charged Particles

- Systematic Errors not shown

- Phobos Preliminary

- PT Distribution of Charged Particles

-  Phobos measures from pT, = 0.030 – 5 GeV/c & beyond

**AuAu**

- Mark D. Baker

## Comparing Au+Au spectra to pp

- Mark D. Baker

## Ratio of Au+Au and pp spectra at 200 GeV

- High pT hadrons don’t scale like Ncoll either!

- mid-peripheral

- central

- Npart = 65 ± 4

- Npart = 344 ± 12

-  arXiv:nucl-ex/0302015

- Mark D. Baker

## A-dependence of Charged Spectra

**Normalize by <N****part****>/2**
**Divide by the value at N****part****=65**

- Mark D. Baker

## Particle Production Scales with Nparteven at high pT

- Normalize by Npart/2. Divide by the value at Npart=65

- Collision scaling would imply:

**PHOBOS**

**Au+Au 200 GeV**

**UA1 pp  (200 GeV)**

- Particle Production Scales with Nparteven at high pT

-  nucl-ex/0301017

- Mark D. Baker

## Approximate Npart scaling at high pT is MAXIMAL suppression! 

- Ncoll * / V ~ Npart4/3 / L ~  Npart

**Only hadrons produced on **
**    ****the surface survive!**

**NOTE: Very peripheral collisions should**
**recover N****coll**** scaling**

- Mark D. Baker

## Is final state “jet quenching” the only explanation?

**Particle Yield/<Npart/2>**

**Initial state parton saturation works too ...**

**Kharzeev, Levin, McLerran **
**hep-ph/0210332**

- Mark D. Baker

## How do we resolve this?

- Strong (maximal) final state suppression at high pT?
- Indication of high density strongly interacting matter!
- Strong initial state suppression persisting to moderately high pT?
- Indication of multipartonic effects in the nuclear wavefunction!

**dAu data!   **** Prediction: **
**Saturation: R****dAu**** ~ 0.75 for 15% central dAu**

**Kharzeev, Levin, Nardi  hep-ph/0212316**

- Mark D. Baker

## Centrality determination in d+Au

**Centrality in d+Au: Handle with care!**

**HIJING d+Au MC**

**HIJING d+Au MC**

- Mark D. Baker

## Preliminary Results from d+Au

- Mark D. Baker

## Preliminary Results from d+Au

**Preliminary Results from d+Au**

- Mark D. Baker

## Preliminary Results from d+Au

**KLN**
**Saturation**

- Mark D. Baker

## Global Observations from PHOBOS

- Empirical Scaling Rules
- Overall particle production in AuAu (low pT):
- “Hard” component does not grow with energy.
- Limiting fragmentation (“xF scaling”) seen in AuAu.
- Overall particle production scales like Npart
- Particle production/participant pair looks like e+e-
- Behavior at moderately high pT
- _Maximal_ suppression from Ncoll scaling in AuAu.
- Ncoll scaling (or slight enhancement) in dAu
- Centrality dependence in dAu
- Ncoll scaling even for 20% most central data!
- Increasing suppression from Ncoll scaling at low pT

- Mark D. Baker

## Conclusions

- PHOBOS “scaling rules” provide many pieces of the puzzle.
- The latest news from PHOBOS:
- We have compared _central_ AuAu to _central _dAu.
- This data strongly disfavors the “initial state” parton saturation interpretation of high pT hadron suppression.

- Mark D. Baker

## Backup slides

- Mark D. Baker

## This Year: PHOBOS Detector 2003

**This Year: PHOBOS Detector 2003**

-  Moved TOF walls back ~ 5 m from interaction point

-  Installed new spectrometer trigger detector that selects on high pT tracks

-  Installed new “time-zero” (T0) Cerenkov detectors to provide triggering and on-line vertexing as well as a start time for our TOF walls.

-  Proton calorimeter on Gold and Deuteron “going” sides for dA run

- SPECTRIG

- mini-pCal

- pCal

- Mark D. Baker

## Initial state parton saturation?

**See Iancu, Leonidov, McLerran  hep-ph/0202270**

** ****Gluon density cannot grow indefinitely.**
** ****Non-Abelian diagram gg********g kicks in at****                                            low x or low k********.**

- Mark D. Baker

## Centrality scaling in pT bins (Au+Au)

- Centrality scaling in pT bins (Au+Au)

- Spectra normalized to a fit at mid-peripheral 45-50% bin.

-  Over the centrality range studied, for low and high pT, the Au+Au data scale approximately with number of participants.

-  nucl-ex/0302015; Submitted for Publication

- Mark D. Baker

## Spectrometer Performance

- Data Sample Production Run 2001(200 GeV)
- 7.8 M Au+Au Events, Min. Bias Trigger
- 32 M reconstructed particles

**Acceptance**

**Momentum Resolution**

- Mark D. Baker

## Centrality Determination (AuAu)

**Data**

**Paddle signal**

**N****participants**

**Data+MC**

** ****HIJING +GEANT**
** ****Glauber calculation**
** ****Model of paddle trigger**

- Mark D. Baker

## PHOBOS Preliminary Results from d+A

- PHOBOSpreliminary

- PHOBOS
- preliminary

- PHOBOS
- preliminary

- PHOBOS
- preliminary

**R****dAu**

**R****dAu**

- Mark D. Baker

## Remove the “Leading Proton” Effect 

- Remove the “Leading Proton” Effect

******s**

******s****eff**

- Basile et al (1980-1984)

- pQCD e+e- Calculation

- (A. Mueller,
-  1983)

- Mark D. Baker

## Many ways to slice pz

**Rapidity: Generalized velocity**

**Pseudorapidity: ~y: easier to measure**

**Feynman x: scaled p****z**

- Mark D. Baker