# Presentation: 671416

## 0 with high pT

******0**** with high p****T**
**in p+p, d+Au and Au+Au Collisions **
** ****Measured by the PHENIX Experiment*** *

**Henner B****ü****sching**
**Brookhaven National Laboratory**
** ****Hot-Quarks Workshop, Taos, July 23, 2004*** *

## High pT Particle Production

**High p****T**** Particle Production**

**Mapping contributions of**
**Initial-state effects**
**Final-state effects**

**Possible initial-state effects:**
**Initial-state multiple soft scatterings                             ****(Cronin effect)****                        **** *****R*****AA**** > 1**
**Modifications of nuclear structure functions in nuclei ****(Shadowing)****                            *****R*****AA**** < 1**
**Gluon-saturation                   ****(Color Glass Condensate)****      *****R*****AA**** < 1 ?**

**Final-state effects**
**dense partonic medium ****parton energy loss (and recombination)**
**    ****(Jet Quenching)**
**Dense hadronic medium ****hadronic energy loss**

##  PHENIX-Setup

-  **PHENIX-Setup**

**Relevant for this talk:**
**Detectors in the central spectrometer arms **
** ********0**** via ********0 ******
**Lead-scintillator calorimeter (****PbSc****)**
**Lead-glass calorimeter (****PbGl****)**
**Centrality, vertex**
- Beam-Beam Counter (**BBC**)   	 3.0 < || < 3.9
- Zero-Degree Calorimeter (**ZDC**)

**(pseudorapidity |********| < 0.35)**

## 0 production in p+p

**Constrains Fragmentation Function ****D(Gluon-pi)**
**Reference for Au+Au spectra**

******0**** production in p+p**

- Phys. Rev. Let 91, 241803 (2003)

******AB ********hX** ** ****f****a/A****(x****a****,Q****2****a****)** ******f****b/B****(x****b****,Q****2****b****)****       **
- ******a b ********cd**** ** **D****h/c****(z****c****,Q****2****c****)**

**Good agreement with NLO pQCD **
- Factorization theorem:

***KKP***
***Kretzer***

**data vs pQCD**

**200 GeV - Run2 **

## 0 Spectra in Au+Au at 200 GeV

******0**** Spectra in Au+Au at ****200 GeV**

- Particle
- Physics

**central**

- Nuclear
- Physics

**peripheral**

- spectra up to 15 GeV/c

**Use p+p as base line measurement**

- Phys. Rev. Lett. 91, 072301 (2003)

**p****T**** (GeV)**

## Nuclear Modification Factor RAA

- Phys. Rev. Lett. 91, 072301 (2003)

**integrated ********0**** yield **
**above p****T**** = 4 GeV/*****c***

## Jet Quenching?

**Jet Quenching?**

** ********0**** suppression described by models ****	****	****        with parton energy loss**
**Additional nuclear effects needed to describe ****	****            *****p*****T**** dependence**
**Other explanations not ruled out at this stage**

**without parton energy loss**

**with parton energy loss**

- Wang

- Wang

- Levai

- Levai

- Vitev

**Comparison with model calculations with and without parton energy loss:**

**d+Au**

## The Control Experiment: d+Au

**The Control Experiment: d+Au**

**No suppression in d+Au**
**Initial-state effects ruled out as explanation for suppression in Au+Au**

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

**p****T**

**R****AB**

**1**

- ~2-4 GeV/c

- Gluon Saturation

- Jet Quenching Models

- d+Au  at *s**NN* = 200 GeV

## 0's in d+Au: Data vs. pQCD

******0****'s in d+Au: Data vs. pQCD**

**Data well reproduced by**
**NLO pQCD calculation, plus**
**Phenomenological model of Cronin-Effect, plus **
**Shadowing**** **

- Levai et al., nucl-th/0306019

- Kopeliovich et al., Phys. Rev. Lett. 88, 232303 (2002)

##  d+Au – centrality dependence

**Phenix preliminary**

## RdAu for different centralities

**R****dAu**** for different centralities**

- Qualitative agreement with model by Accardi and Gyulassy.                     Partonic Glauber-Eikonal approach: sequential multiple partonic collisions.         nucl-th/0308029 v2

**Phenix preliminary**

## Centrality Dependence in d+Au

**Au + Au Experiment**

**d + Au Control Experiment**

- opposite behavior with increasing centrality in Au+Au and d+Au
- RAuAu decreases
- RdAu charged increases
- RdAu ********** **increases

- Preliminary Data

- Preliminary Data

- Final Data

**charged**

******0**

## Central to Peripheral

**Phenix preliminary**

## RAA for 0 in Central CollisionsDifferent Energies

- A.L.S.Angelis, PLB 185, 213 (1987)
- WA98, EPJ C 23, 225 (2002)
- [ Renormalization: D.d'E. nucl-ex/0403055]
- PHENIX, PRL 88 022301 (2002)
- PHENIX, PRL 91, 072303  (2003)

**63 GeV Au+Au**

## 0 Spectra at 62 GeV

******0**** data in min. bias, 0-10% ,and 10-30% central collisions up to 7GeV/c**
**Small systematic uncertainty : 9~12%**

**Phenix preliminary**

## 62 GeV p+p Reference for 0

******0**** ****reference**

**Talk by David d’Enterria**

- +/-25% uncertainty

**(charged**** ****reference)**

******0**** ****reference**

## RAA for 0 at 62GeV

**R****AA**** for ********0**** at 62GeV**

******0**** ****reference is used here**

**Ratios close to unity  at p****T****~2.5 GeV/c, **
**then decreases**
** ****Same tendency as   200 GeV Au-Au**
** ****less suppression at intermediate p****T****.**

## RAA for 0 at 62GeV: suppression predictions

**I. Vitev nucl-th/0404052**

**Adil & Gyulassy nucl-th/0405036**

**R****AA**** (****π****0****) ~ 0.5 - 0.3**

**R****AA**** for ********0**** at 62GeV:**** ****suppression predictions**

## RAA for 0 at 62 GeV

******0**** ****reference **
**is used here**

- Vitev
- nucl-th/0404052

-  **Reasonably good agreement (esp. high p****T****) within uncertainties **
** ****Uncertainty in the p****T**** shape (esp. low p****T****) of p+p reference ...**

## RAA for 0 at 62GeV

**charged**** ****reference**
**+ h/********  ratio is used here**

**Agreement with charged**** ****reference better:**
**Better p+p reference needed**

## RAA for charged hadron

** ********0**** yield is multiplied by 1.6**
**discrepancy between charged and ********0**
**Pions more suppressed than h+/- at intermediate pT**
**Large proton contribution up to at least 4GeV/c**

******0**

**charged**

**charged**

******0**

- 0-10%

- 10-30%

**charged**** ****reference **
**is used here**

**62.4 GeV  **

## RAA for 0 in Central CollisionsDifferent Energies

- A.L.S.Angelis, PLB 185, 213 (1987)
- WA98, EPJ C 23, 225 (2002)
- [ Renormalization: D.d'E. nucl-ex/0403055]
- PHENIX, PRL 88 022301 (2002)
- PHENIX, PRL 91, 072303  (2003)

## Summary

** ********0**** at  200 GeV p+p **
** ********0**** at 62.4 and 200 GeV Au+Au**
** ********0 ****at 200 GeV d+Au**
**Centrality dependence**
**Inclusive spectra**** suppressed ****in Au+Au**
**by a factor of 4-5 at 200 GeV**
**by a factor of ~3 at 62.4 GeV**
**No suppression in 200 GeV d+Au**
**Onset of suppression “smooth” with centrality ****	****	****    ****	****	****and probably cm energy**
**Stay tuned: Always something new from PHENIX...**

## Slide 24