# Presentation: 593665

## Neutral Pions and Charged Hadrons with Large Transverse Momentum in Au+Au and d+Au Collisions at sNN = 200 GeV

-  Quark Matter 2004
- Oakland, January 13th

**Christian Klein-Bösing**
**IKP Münster**
**for the PHENIX Collaboration**

## PHENIX-Measurement of High pT  Particles in Au+Au and d+Au Collisions at sNN = 200 GeV

-  Quark Matter 2004
- Oakland, January 13th

**Christian Klein-Bösing**
**IKP Münster**
**for the PHENIX Collaboration**

## Particle Production at High pT

**General**
***Hard**** *processes: Parton collisions with large Q2 (“Jets”)
- Factorization:
- PDF  pQCD FF
**p+p**
- Fragmentation into QCD-vacuum
**Au+Au**
- Early reaction-phase
- Probe for a later hot and dense phase

**Medium influences:**
- “Jet”-like  correlations
- Particle ratios
- Particle yields

## Nuclear Modifiction Factor

**Glauber model:**
- AA/dA incoherent superposition of NN
**Comparison with      scaled NN**
- RAA  1 (for pT > 2 GeV) ?
- Deviation  medium effects ?

*b*

- nuclear overlap function
*"Nucleon-Luminosity"*

## Known Effects NA

**Multiple soft scattering**
- Broadens pT spectrum
- Cronin Effect
**Change of the nuclear structure function / PDF **
- Shadowing (RAA < 1)
- Anti-shadowing (RAA > 1)

## 0's @ PHENIX

**Reconstruction ********0********2******
- All pair combinations
- Invariant mass
***m******inv****** =***** ******** *****2E1E2 (1- cos***** ******** ******** 135 MeV**
- Combinatorial background:
- “Mixed events”
***1* from current event *2* from old event
**Corrections**
- Acceptance
- Efficiency

## Charged Particles @ PHENIX

**Tracking in west arm**
- Momentum reconstruction with BBC,PC1 and DC
**Background rejection**
- Matching PC2 and PC3 hits
- Remaining background:
- Conversions and decays
- Determined and subtracted statistically
**Corrections**
- Acceptance, decay in flight
- Efficiency

**h****+**

## Signal/Background

******0  ****analysis limited by statistics**
- Further improvement with high pT photon triggers
**Charged particle analysis limited by background:**
- p/p = 0.7% 1.1%p (GeV/c)
- Background from conversion electrons hardly seperable from charged 

- minimum Bias Au+Au

## Au+Au @ sNN= 200 GeVat Midrapidity

**Au+Au @ ********s****NN****= 200 GeV****at Midrapidity**

- Poster V. Pantuev P33

## Peripheral Au+Au Compared to Scaled p+p

**consistent with **
**N****coll**** scaling**

## Central Au+Au Compared to Scaled p+p

**factor 5 suppression**** **

**factor 2 difference**** **

## h/ Ratios

**h/******** Ratios**

**Expectation (pp, e****+****e****-****):**
- h/  1.6
**Only the case in peripheral collisions and above 5GeV**
**Identified Hadrons**
- Anomalous p/
- Data suggests baryon vs. meson effect (from ,p vs ,)
- Talks: F. Matathias
**Approaches**
- E.g. recombination of quarks in a thermal phase

- Au+Au @ 200AGeV

- nucl-ex/0310005

## Possible Explanations

**Possible Explanations**

**Jet quenching**
- Hard scattered partons lose energy via gluon-bremsstrahlung
- Depends on color charge density
- Depends on traversed distance in medium (correlations)

## But .....

**Effects of cold nuclear matter (“initial state”) at ********s****NN**** = ****200 GeV unknown**
- Shadowing
- Gluon Saturation

- d+Au needed as reference case:
- No produced medium...

## d+Au @ PHENIX

**d+Au @ PHENIX**

**No suppression in d+Au collisions @ ********s****NN**** = 200 GeV**
- PRL 91, 0723903 (2003)
**Similar results from STAR, PHOBOS, BRAHMS**

-  Initial state effects excluded

- d+Au, Au+Au at *s**NN* = 200 GeV

## RdA for 's

-  in d+Au 7 < pT  8

- Poster
- p+p: V. Hiejima D6
- Au+Au: S. Mioduszewski P8

## RdA for 's

**Similar to ********0**
**No obvious mass dependence for mesons**

## d+Au Spectra at Midrapidity

**d+Au Spectra at Midrapidity**

- Poster H. Büsching P4

## Centrality Dependence at Midrapidity

**Centrality Dependence at Midrapidity**

## Centrality Dependence at Midrapidity

**Centrality Dependence at Midrapidity**

## Centrality Dependence at Midrapidity

**Centrality Dependence at Midrapidity**

## Centrality Dependence at Midrapidity

**Centrality Dependence at Midrapidity**

## Centrality Dependence 

**Examine nuclear modification at fixed p****T**
- Enhancement in central d+Au
- Suppression in central Au+Au
- Deviation from scaled pp vanishes in peripheral collisions

- central

- peripheral

- Strong medium effects in central
- Au+Au overcome initial Cronin enhancement

## Does the Enhancement Vanish at High pT ??

**R****CP**
- Compares Yields in central and peripheral scaled by Ncoll
- Many systematics cancel
**Different parts of PHENIX measure different p****T ****ranges of ******
**Enhancement in central vanishes at high p****T**** **

- Poster J. Jia P3

## Conclusion

**Observation: Suppression of high p****T**** charged hadrons  and ********0****'s in central Au+Au**
- Suggests medium induced energy loss
**Enhancement/absence of suppression at midrapidity in d+Au**
- As expected from cronin effect
- Rules out initial state effects for observed suppression in Au+Au
**Established baseline for the effects of cold nuclear medium at ********s****NN**** = 200 GeV**

##   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**
**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

## Phenix @ RHIC

**Central Arms**
- || < 0.35
- Calorimetrie (PbSc PbGl)
- Tracking (PC, DC)
- PID (RICH,TOF)
**North and South Arms**
- Muon PID and Tracking
**Global**
- Trigger (BBC)
- Centrality (BBC, ZDC)

## Corrections

**Geometrical acceptance**
**Detector effects**
- Multiplicity
- Energy- / position resolution
**Analysis cuts**
- Asymmetrie
- PID
- Bad modules

**Efficiency:**
**From embedding of simulated**
******0**** into real events**

##  in Au+Au

## d+Au Centrality Dependence

**d+Au Centrality ****Dependence**

**Centrality Selection with BBC-South **
- Au going side
- 3 <  || < 3.9
- Charge sum  multiplicity
**N****coll**** **** ****from Glauber model**

- Au

- d

## Recombination

**Two competing processes for hadron production**
- Jet fragmentation
- Recombination of 3 quarks or a quark/anti-quark pair in a densely populated phase space
** ****Fries et al.:**
- In case of thermalized partons fragmentation wins over recombination only above           5 GeV/c
- Explains p/ ratio
- “Such a phase may be appropriately called a QGP”

**ede**

- Fries, et al, nucl-th/0301087

- also, Greco, Ko, Levai, nucl-th/0301093

## 0 Peaks

- 2 GeV  pT  2.5 GeV
- 134 939  3184 0  from
- 26 M minimum bias events (PbGl)

## Centrality Dependence 0

**Examine nuclear modification at fixed p****T**
- Enhancement in central d+Au
- Suppression in central Au+Au
- Deviation from scaled pp vanishes in peripheral collisions

- central

- peripheral

- Strong medium effects in central
- Au+Au overcome initial state Cronin enhancement

## Theory Comparison

**Prediction from pQCD **
- Tuned to pp (<kT2>...)
- Good qualitativ agreement with expactation from Cronin enhancement
- Further improvement with inclusion of shadowing
**Prediction from saturation models**
- Fails, no suppression in central d+Au at midrapidity
- Different rapidity region
- PHENIX