# Presentation: 593679

## Systematic Study of Particle Production 

**IKP Münster**

- 22nd Winter Workshop on Nuclear Dynamics
- La Jolla, San Diego
-  March 11th-19th 2006

**Systematic Study of Particle Production **
**at High p****T ****with PHENIX**

## Why High pT?

**Studying *****hard***** processes**
- Parton collisions with large *Q**2* (*~ p**T**2*)
- Factorization:
**p+p**
- Fragmentation into QCD-vacuum
**Au+Au**
- Early reaction-phase
- Probe for a later hot and dense phase

**Quantifying the medium influence (Step 1)**
- Single particle (incl.) spectra
- Leading hadron carries large fraction of initial parton momentum

## Why High pT?

**Studying *****hard***** processes**
- Parton collisions with large *Q**2 *(*~ p**T**2*)
- Factorization:
**p+p**
- Fragmentation into QCD-vacuum
**Au+Au**
- Early reaction-phase
- Probe for a later hot and dense phase

**Quantifying the medium influence (Step 1)**

## How High is “High” pT?

**First year of RHIC  (130 GeV Au+Au):**
*p**T*= 4 GeV/*c* was high
**Where hard scattering is the dominant source of particle production (power law spectrum)**
**Consider mainly *****p******T***** > 6 GeV/*****c***
**Main source of information ********0****, ********, ******
- Identified particles
- Test different aspects of the medium
- Mesons from parton fragmentation
- Direct photons also produced in hard scatterings
- And thermal radiation, jet-plasma interaction etc. (talk by **Oliver Zaudtke**)

- “Suppression of Hadrons with **Large** Transverse Momentum in
- Central Au+Au Collisions at sqrt(s) = 130 GeV” (PRL 88,022301 (2002)

## 0,  and direct  @ PHENIX

**Measurement with the EMCal**
- Two different detector types
**Reconstruction**
- 0 () 2
- Invariant mass
***m******inv****** =***** ******** *****2E******1******E******2 ******(1- cos***** ********) ******** 135 (548) MeV**** **
**Combinatorial Background:**
- Determination via “mixed event” technique
- Photons from different events a priori uncorrelated

** ****Direct ******** more sophisticated**
- Subtraction of all decay photons
- Tagging etc.

## The Baseline @ 200 GeV

**Remarkable agreement with NLO pQCD**
- Even sensitiv to choice of fragmentation function *FF(g****)*
**Measured by the same experiment! **

- PRL **91**, 241803 (2003)

## PHENIX High pT Highlights

**Suppression of high *****p******T***** hadrons**** in central Au+Au relative to scaled p+p **
**Also seen in charged hadrons**
**Initial state or final state?**

- PRL **91**, 072301 (2003)

## PHENIX High pT Highlights

**No suppression in d+Au collisions**
**Initial state effects ruled out as explanation for observed suppression**
- No effects of CGC at *y *= 0
**Difference between charged hadrons and ********0**** at intermediate *****p******T***
- Coalesscence/recombination of quarks from thermal source?

- d+Au, Au+Au at *s**NN* = 200 GeV

- PRL **91**, 072303 (2003)

## PHENIX High pT Lights

**Direct Photons**
**Ultimate test for hard scatterings**

- PRL **94**, 232301 (2005)

## PHENIX High pT Lights

**Direct Photons**
**Ultimate test for hard scatterings**
**No suppression of direct photons in central Au+Au**
**Strong final state effect**

- PRL **94**, 232301 (2005)

## Common Explanation

**Partons lose energy by (coherent) gluon Bremstrahlung in the medium: **
- Gluon density can be constrained via multiplicity
**Average energy loss can be determined from spectrum shift (*****R******AA*****)**

**For power law:**

## Single Particle Spectra @ High pTThe First Three Years

**p+p**

**d+Au**

**Au+Au**

**130 GeV**

**200 GeV**

## What else can be done at high pT?

**More differential studies of the (existing) data at high *****p******T***
- Finer bins in centrality (use of high-*p**T* trigger)
- Different particle types (e.g.
- Quark-mass dependence, heavy flavor (talk by **Cesar Luis da Silva**)
- Jet correlations (talk by **Nathan Grau**)
- Reaction plane (*L*) dependence (talk by **Dave Winter**)
**New Au+Au data**
- Improve *p**T*-reach
**Vary the collision energy**
**Vary the system size**

## Mass dependence at high pT

**Mass dependence at high p****T**

****** ****same quark content as ********0**
**Factor 4 heavier**

- nucl-ex/0601037

## Mass dependence at high pT

**Mass dependence at high p****T**

****** ****same quark content as ********0**
**Factor 4 heavier**
**Same *****R******AA***** as ********0**
- Suppression does not depend on hadron-mass

- nucl-ex/0601037

## Mass dependence at high pT

**Mass dependence at high p****T**

****** ****same quark content as ********0**
**Factor 4 heavier**
**Same *****R******AA***** as ********0**
- Suppression does not depend on hadron-mass
******/********0**** similar for all colliding species and centralities**
- Suppression happening at the partonic level
- Fragmentation function not strongly influenced by the medium

- nucl-ex/0601037

## System Size Dependence...

**System Size Dependence...**

## System Size Dependence

**Variation of centrality **
- Onset of suppression:      	*N**part*  50
- No good discrimination in 	Au + Au

- PRL **94**, 232301 (2005)

## System Size Dependence

**Variation of centrality **
- Onset of suppression:      	*N**part*  50
- No good discrimination in 	Au + Au
**Cu+Cu (*****A***** = 64****)**
- Finer  *N**part* “resolution”
- Different geometry
- Surface/volume effects

- PRL **94**, 232301 (2005)

## The Measurement in Au+Au

**New RHIC Run4 Au+Au data**
**Sampled 241 ********b****-1**
- 1.5 B events
**Spectra up to 20 GeV/c **

**p****T**** (GeV/c)**

## The Measurement in Au+Au

- Suppression stays nearly constant up to 20 GeV
- Consistent with *dN**g**/dy* ~ 1200 calculation

## The Measurement in Cu+Cu

**RHIC Run5 (2005)**
**59 M minimum bias events**
**1.9 M high-p****T**** triggered **
- 2.2 B events sampled
**Spectra up to 18 GeV/c **

## The Measurement in Cu+Cu

- Central Cu+Cu also suppressed
- Consistent with energy-loss calculation *dN**g**/dy* = 370

## Au+Au vs. Cu+Cu

**Au+Au vs. Cu+Cu**

## Au+Au vs. Cu+Cu

- Suppression pattern identical at same *N**part*

**Au+Au vs. Cu+Cu**

## Centrality DependenceIntegrated RAA

**Similar *****N******part***** dependence**
**Hints for different slope**
- Surface effects?

## Centrality DependenceIntegrated RAA

**Path length and density dependent**
- Fixed to central Au+Au
- No surface effects
**Fair agreement but trend in Cu+Cu missed**

- hep-ph/0603010

## Centrality DependenceIntegrated RAA

**Geometrical model with “corona” effect**
- More jets from surface
- Correlated with ellepticity
- Minimal for sphere

## Centrality DependenceIntegrated RAA

**Geometrical model with “corona” effect**
- More jets from surface
- Correlated with ellepticity
- Minimal for sphere

**Au+Au**
**30-40%**
***N******part***** ****= 114**

**Cu+Cu**
**0-10%**
***N******part***** ****= 98.2**

## Energy Dependence...Going down!

**Energy Dependence...****Going down!**

## Au+Au @ 62.4 GeV

**RHIC Run4**
- 40M Events
******0**** production also suppressed**
- Reasonable agreement with theory (*dN**g**/dy* ~ 650-800)
- Vitev: Phys. Lett. B **606 **(2005) 303
- N.B.: p+p reference not measured at RHIC, large  uncertainties (shape)

- 0

## p+p Reference @ 62 GeV

- J.Phys.G31:S491-S512,2005

## p+p Reference @ 62 GeV

- J.Phys.G31:S491-S512,2005

## Cu+Cu @ 22.4 GeV (Premiere)

**Go near SPS Energies**
- p+p data at 21.7 – 23 GeV
- Use of parameterization as reference
**3 days of RHIC Run5**
- 6.8M Events after quality cuts
- Centrality via PC1 multiplicity

- 0

## p+p Reference @ 22 GeV

## p+p Reference @ 22 GeV

## 0 RAA 40-50%

*N**coll* = 22.9 4.4 *N**part** *= 23.1 3.3

**PbSc**

**PbGl**

- Uncertainty in *N**coll* and p+p param. (20%)

## 0 RAA 20-40%

**PbSc**

**PbGl**

*N**coll* = 48.4 6.5 *N**part* = 41 3.6

## 0 RAA10-20%

**PbSc**

**PbGl**

*N**coll *= 93.6 9.4* N**part* = 67.8 3.1

## 0 RAA 0-10%

**PbSc**

**PbGl**

*N**coll* = 140.7 14.8 *N**part* = 92.2 2.2

## Excitation Function

**PHENIX/RHIC does SPS Physics**

- nucl-ex/0504001

## WA98 vs. PHENIX

**Similar N****part**** (WA98 : 132, PHENIX: 140)**
**same behaviour**

## What's next?

**Cu+Cu @ 200 GeV**
- 
**Cu+Cu @ 62.4 GeV**
-  and 0
**p+p @ 62.4 GeV**
- Current RHIC run
- Essential baseline
**p+p @ 22.4 GeV**
- Hopefully this RHIC Run?

**Work in progress**

## Single Particle Spectra @ High pTThe First Three Years

**p+p**

**d+Au**

**Au+Au**

**130 GeV**

**200 GeV**

## Single Particle Spectra @ High pTToday

**p+p**

**d+Au**

**Au+Au**

**Cu+Cu**

**22.4 GeV**

**62.4 GeV**

**130 GeV**

**200 GeV**

- Run6?

- Run6

## Summary

**Particle suppression in Au+Au**
- 0  *R**AA* flat up to *p**T* = 20 GeV/*c*
-  and 0 show same suppression pattern
**System Size Dependence**
- Similar *R**AA** *for Cu+Cu and Au+Au for similar *N**part*
- Hints for surface/corona effects
*********s******NN***** dependence**
- Follows expectation from energy-loss models
- RHIC/PHENIX able to do SPS Physics
- First systematic study of jet quenching from ***s**NN** ~ 20 – 200 GeV** * within the same experiment

##   USA   Abilene Christian University, Abilene, TX 

**  ****USA   Abilene Christian University, Abilene, TX **
**             ****Brookhaven National Laboratory, Upton, NY **
**             ****University of California - Riverside, Riverside, CA**
**             ****University of Colorado, Boulder, CO**
**             ****Columbia University, Nevis Laboratories, Irvington, NY**
**             ****Florida State University, Tallahassee, FL**
**             ****Florida Technical University, Melbourne, FL**
**             ****Georgia State University, Atlanta, GA**
**             ****University of Illinois Urbana Champaign, Urbana-Champaign, IL**
**             ****Iowa State University and Ames Laboratory, Ames, IA**
**             ****Los Alamos National Laboratory, Los Alamos, NM**
**             ****Lawrence Livermore National Laboratory, Livermore, CA**
**             ****University of New Mexico, Albuquerque, NM **
**             ****New Mexico State University, Las Cruces, NM**
**             ****Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY**
**             ****Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY    Oak Ridge National Laboratory, Oak Ridge, TN**
**             ****University of Tennessee, Knoxville, TN  **
**             ****Vanderbilt University, Nashville, TN****	**

**Brazil        University of São Paulo, São Paulo**
**China        Academia Sinica, Taipei, Taiwan**
**                  ****China Institute of Atomic Energy, Beijing**
**             ****Peking University, Beijing**
**Czech       Charles University, Prague**
**Republic  Czech Technical University, Prague**
**                  ****Institute of Physics, Academy of Sciences of the Czech, Prague**** **
**France      LPC, University de Clermont-Ferrand, Clermont-Ferrand**
**                  ****Dapnia, CEA Saclay, Gif-sur-Yvette**
**                  ****IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay          **
**                  ****LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau**
**                  ****SUBATECH, Ecòle des Mines at Nantes, Nantes**
**Germany  University of M****ü****nster, M****ü****nster**
**Hungary   Central Research Institute for Physics (KFKI), Budapest**
**                  ****Debrecen University, Debrecen**
**                  ****Eötvös Loránd University (ELTE), Budapest **
**India          Banaras Hindu University, Banaras**
**                  ****Bhabha Atomic Research Centre, Bombay**
**Israel         Weizmann Institute, Rehovot**
**Japan        Center for Nuclear Study, University of Tokyo, Tokyo**
**                  ****Hiroshima University, Higashi-Hiroshima **
**                  ****KEK, Institute for High Energy Physics, Tsukuba **
**                  ****Kyoto University, Kyoto**
**                  ****Nagasaki Institute of Applied Science, Nagasaki**
**                  ****RIKEN, Institute for Physical and Chemical Research, Wako**
**                  ****RIKEN-BNL Research Center, Upton, NY    ****        ****  **
**	****     ****Rikkyo University, Tokyo, Japan             **
**                  ****Tokyo Institute of Technology, Tokyo**
**                  ****University of Tsukuba, Tsukuba **
**                  ****Waseda University, Tokyo                    **
**S. Korea   Cyclotron Application Laboratory, KAERI, Seoul**
**                  ****Kangnung National University, Kangnung**
**                  ****Korea University, Seoul **
**                  ****Myong Ji University, Yongin City **
**                  ****System Electronics Laboratory, Seoul Nat. University, Seoul**
**                  ****Yonsei University, Seoul**
**Russia      Institute of High Energy Physics, Protovino **
**                  ****Joint Institute for Nuclear Research, Dubna **
**                  ****Kurchatov Institute, Moscow**
**                  ****PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg**
**                  ****St. Petersburg State Technical University, St. Petersburg**
**Sweden     Lund University, Lund**

## Backup Slides

**Backup Slides**

## WA98 vs. PHENIX

**Similar N****part**** (WA98: 132, PHENIX: 140)**
**same behaviour!! **

## 0s in d+Au

**PHENIX preliminary**

## 0s in d+Au

**<k****T****>= 0.52 GeV****2**

- Accardi, Gyulassy. Partonic Glauber-Eikonal approach: sequential multiple partonic collisions.
- Phys. Lett. B **586** (2004) 244.  Centrality dependence not very well reproduced

**PHENIX preliminary**

## 0s in d+Au

**<k****T****>= 0.52 GeV****2**

- Kharzeev, Kovchegov, Tuchin, Phys. Rev. D **68, **094013 (2003):
- Saturation scale can influence particle Production even for Qs < kT ...

**PHENIX preliminary**

## Direct Photons in d+Au

**Direct Photons in d+Au**

**Directly sensitive to gluon distribution**
**No effect at high p****T **
- Large uncertainties

-   s

## Npart(x,y)

**Preliminary Plots...**

- ellipticity different

- Transverse *N*part density for similar <*N*part> in Au+Au and Cu+Cu

## Single Particle Inclusive SpectraWhat's New?

**p+p**

**d+Au**

**Au+Au**

**130 GeV**

**200 GeV**

## Single Particle Inclusive SpectraWhat's New?

**p+p**

**d+Au**

**Au+Au**

**130 GeV**

**200 GeV**

## Single Particle Inclusive Spectra

**p+p**

**d+Au**

**Au+Au**

**Cu+Cu**

**22.5 GeV**

**62.4 GeV**

**130 GeV**

**200 GeV**

- Run6?

- Run6

## Single Particle Inclusive Spectra

- p+p

- d+Au

- Au+Au

- Cu+Cu

- 22.5 GeV

- 62.4 GeV

- 130 GeV

- 200 GeV

## Common Explanation

**Partons lose energy by (coherent) gluon Bremstrahlung in the medium: **
- Gluon density can be constrained via multiplicity
**Average energy loss can be determined from spectrum shift (*****R******AA*****)**

**For power law:**