Identified Charged Hadron
Masahiro Konno (Univ. of Tsukuba)Production at RHIC-PHENIX
for the PHENIX Collaboration
konno@rcf.rhic.bnl.gov

Physics motivation
Nuclear Modification Factor RAA

Yield AA/"N binary # AA
R AA =
Yield ppnucl-ex/0603010

Au+Au 200 GeV!

- High-pT suppression due to parton energy loss in themedium (jet quenching).
- The suppression patterns depend on particle type. Protons
are enhanced, while pions and kaons are suppressed.

Baryon Enhancement
Ratio

PRL 91, 172301 (2003)

v2- p/π ratio ~1 for central Au+Au at intermediate pT (2-4 GeV/c).
- Larger than expected from jet fragmentation (measured in pp, e+e-).
- Baryon / Meson difference at intermediate pT.
(on RAA (nuclear modification factor) , v2 (elliptic flow) etc.)

Quark Recombinationp/π

At intermediate pT, recombinationof partons may be a more efficientmechanism of hadron production
than fragmentation.

Fries, R et al PRC 68 (2003) 044902
Greco, V et al PRL 90 (2003) 202302
Hwa, R et al PRC 70(2004) 024905

A number of models predicted a turnoverin the B/M ratio at pT just above where theavailable data finished…

What we should do:
What is the origin of (anti-)protonenhancement at intermediate pT?
Possible sources (medium effect) :- Strong radial flow
- Recombination of quarks- Baryon junction

pT spectra and particle ratios (Baryon/Meson) provide themost basic tool to investigate the hadronization mechanisms.
To distinguish the different production mechanism for
protons and pions at intermediate and higher pT.

PHENIX detector

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

TOF

Aerogel 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)

PID detectors

No Cutp

K+π+
Aerogel Veto

Clear Proton Line!

Results

Data- Data set: Au+Au 200 GeV (taken in Run4, 2003-2004)
Analysis - 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

pT spectra of (anti-)protons

Identified
with ACC

pT reach extendedfor (anti-)protons
with fine centrality bins.

pbar/p vs. pTCentralPeripheral

No significant
centrality or pT dependence(up to 6 GeV/c).

p/π vs. pT

p/πACC* No feed-down correction.
* p+p data (nucl-ex/0603010)

p/π

p/π vs. pT (centrality dep.)

ACC

p/π

p/π

CentralPeripheral- p/π (pbar/π) ratios seem to turn over at intermediate pT,
and close to the value of fragmentation at higher pT.
- Indicating transition from soft to hard at intermediate pT.

Proton RCPR CP =Yield Central/"N binary # Central
Yield Peripheral/"N binary # Peripheral

TOF!

- Proton RCP shows unity above 2 GeV/c.
- Peak structure at 2~3 GeV/c.
- Proton RCP seems to show decreasing above 3 GeV/c.
- Expected to merge to pion RCP at higher pT.
- Need more statistics to look at high-pT points.

p/π ratio in 62 GeV Au+Au

62 GeV Au+Au- Rapidly increasing with pT for 62 GeV.
- Weaker centrality dependences than those of 200 GeV.
- Significant difference for p and pbar at 62 GeV.
(Indicating more baryon transport and less p-pbar pair production
at 62 GeV than 200 GeV.)

p/π ratio in Cu+Cu••

p/π+ ratio : decreasing as a function of √sNN.
p/π- ratio : increasing as a function √sNN.
– Cu+Cu 22.5 GeV central data reaches the p+p values.
– Cu+Cu 62.4 GeV central data is higher than that in 22.5 GeV.

Suggests a significant contribution of incoming protons(not by the produced protons) in lower energies Cu+Cu.

Summary- pT reach of PID (especially for p, pbar) extended with:- High statistics 200 GeV Au+Au data
- New PID detector (Aerogel)- Results:- pbar/p ratio No centrality or pT dependence- p/π ratio Indicating transition from soft to hard at intermediate pT- RCP (Anti-)proton RCP shows decreasing above 3 GeV/c- Collision system dependence:- Similar turnover curve on p/π in 62 GeV Au+Au- Npart scaling on particle ratios (Cu+Cu / Au+Au)- Comparison with models:- Recombination models seem to be matchedto the experimental data.
data analysis, reduce sys. errors for PID at high p
Next -- Improve
Analyze Run5 p+p (abundant) data to make R at higher pTAA- MRPC-TOF (σTOF~100ps) to be installed for PID upgradeT