Measurement ofHigh-pT Identified Charged Hadronsin 䌥㼖NN = 200 GeV Au+Au Collisions
at RHIC-PHENIX
Masahiro Konno
Univ. of Tsukuba, for the PHENIX Collaboration

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JPS 2006 Spring (Ehime University, 3/27/2006)

M. Konno

Outline

1. Physics Motivation
2. PHENIX detector
3. Data Analysis- pT spectra measurement- Particle Identification (PID)- Background subtraction

4. Results- pT spectra (proton, antiproton)- pbar/p ratio vs. pT- p/π ratio vs. pT

5. Comparison with models
6. Summary2
JPS 2006 Spring (Ehime University, 3/27/2006)

M. KonnoPhysics Motivationd 2 N AA / dpT d"
RAA ( pT ) =TAA d 2# NN / dpT d"

Nuclear Modification Factor RAA
Au+Au 200 GeV

High-pT suppression due toparton energy loss in the medium(jet quenching).

nucl-ex/0603010!

The suppression patterns dependon particle type. Protons are enhanced,
while pions and kaons are suppressed.
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JPS 2006 Spring (Ehime University, 3/27/2006)

M. KonnoPhysics Motivation

Motivations:

Baryon Enhancement
PRL 91, 172301 (2003)

What is the origin of (anti-)protonenhancement at intermediate pT?
To distinguish the different production
mechanism for protons and pionsat intermediate and higher pT.
Possible sources (medium effect) :- Strong radial flow
- Recombination- Baryon junction- p/π ratio ~1 for central Au+Au at intermediate pT (2-4 GeV/c).
- Larger than expected from fragmentation (measured in pp, e+e-).
- Baryon / Meson difference at intermediate pT.
(on RAA (nuclear modification factor) , v2 (elliptic flow) etc.)4
JPS 2006 Spring (Ehime University, 3/27/2006)

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PHENIX detector

EMCal- Central Arm Detectors(magnetic spectrometer)- Event Characterization detectors

TOFAerogel Cherenkov Counter
Hadron Identification at High pT- n = 1.0113.
- Full installation in 2004.
- Proton separation from 䃖㻒㻮
up to 8 GeV/c.

Drift Chamber(momentum meas.)
Tracking detectors(PC1,PC2,PC3)

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Data Analysis- Data set: Au+Au 200 GeV (taken in Run4, 2003-2004)- High statistics (440M events used)- Charged Hadron PID:
- TOF
- Aerogel (for PID extension toward high pT, Run4-)- MC Simulations:- Acceptance, efficiency (occupancy) corrections- No feed-down correction.
BG Subtraction

3~4 GeV/c

S/N~12

4~5 GeV/c

S/N~5Using residual bendingin φ direction.
Backgrounds:- random association- electrons from photon conversion- decayed products

5~6 GeV/c

S/N~2

6~7 GeV/c

S/N~1

track matching residual (a.u.) 6JPS 2006 Spring (Ehime University, 3/27/2006)

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Results

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pT spectraof (anti-)protons
Work in Progress

Work in Progress

pT reach extendedfor (anti-)protons
with fine centrality bins.
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pbar/p vs. pTWork in Progress

Peripheral

CentralWork in Progress

No significant
centrality or pT dependence(up to 6 GeV/c).
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p/π vs. pTp/πp/πWork in Progress* No feed-down correction.

- p/π (pbar/π) ratios seem to turn over at intermediate pT,
and close to the value of fragmentation at higher pT.
- Still large systematic errors.
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p/π vs. pT (centrality dep.)
Work in Progress* No feed-down correction.

p/πp/πPeripheral

Central- p/π ratios look to have a peak at intermediate pT (2-4 GeV/c).
- Clear peak in central events than that in peripheral.
JPS 2006 Spring (Ehime University, 3/27/2006)

M. Konno11p/π vs. pT (centrality dep.)p/πp/πWork in Progress* No feed-down correction.
* p+p data (nucl-ex/0603010)- Centrality dependence seen in the magnitude.
- p/π ratio in peripheral lies slightly above the p+p ratio.
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Comparison with Models
PRC 69, 034908 (2004)

PRC 68, 044902 (2003)

PRC 67, 034902 (2003)

p/π

PRL 90, 202302 (2003)

p/π- Only look through several models (recombination, hydro+jet, …).
- Novel mechanism of hadron production at intermediate pT. 13
JPS 2006 Spring (Ehime University, 3/27/2006)

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Summary- pT reach of PID (especially for p, pbar) extended with:(1) High statistics Au+Au data
(2) New PID detector (Aerogel)- Results are still work-in-progress.
pbar/p ratio:- No centrality or pT dependence.
p/π ratio:- Centrality dependence seen in the magnitude.
- Indicating transition from soft to hard at intermediate pT.

Next- Improve data analysis, reduce sys. errors for PID at high pT.
- Analyze Run5 p+p (abundant) data to make RAA at higher pT.
- MRPC-TOF (σTOF~100ps) to be installed for PID upgrade.
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Backup slides

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PID demonstrationNo CutAerogel Veto

pK+π+Clear Proton Line !
- Mass square cut 2σ selection on EMCal-TOF.
- With (without) requiring Cherenkov light from Aerogel* Clear pion signal above the threshold (~1 GeV/c).
* Proton separation up to ~7 GeV/c.
JPS 2006 Spring (Ehime University, 3/27/2006)

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Charged pion spectra
identified with ACC

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p/π ratio in Cu+Cu / Au+Au

Central Au+Au

Central Cu+Cu* No feed-down correction.

- Observed a large p,pbar contribution at intermediate pT,
as seen in 200 GeV data.
- Npart dependences on particle ratios have similar trend
as in Au+Au (Npart scaling).
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RAA vs. pT

Npart~98

Npart~114

Cu+Cu 200 GeV
Central (0-10%)

Au+Au 200 GeV
Mid-Central (30-40%)* No feed-down correction.

- Similarity on RAA seen in Cu+Cu and Au+Au:- The magnitude of enhancement/suppression- Particle type dependence
JPS 2006 Spring (Ehime University, 3/27/2006)

M. Konno

19Bump in the h/π ratios
PRC 69, 034910 (2004)- Expectation (pp,e+e-): ~1.6
- Above 5 GeV/c and in peripheral
events: recover normal fragmentation.

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JPS 2006 Spring (Ehime University, 3/27/2006)

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