Measurement of

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Measurement of High-pT Identified Charged
Hadrons in vsNN 200 GeV AuAu Collisions at
RHIC-PHENIX
Masahiro Konno Univ. of Tsukuba, for the PHENIX
Collaboration
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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/? ratio vs. pT 5.
Comparison with models 6. Summary
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Physics Motivation
Nuclear Modification Factor RAA
nucl-ex/0603010
AuAu 200 GeV
The suppression patterns depend on particle type.
Protons are enhanced, while pions and kaons are
suppressed.
High-pT suppression due to parton energy loss in
the medium (jet quenching).
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Physics Motivation
Motivations
Baryon Enhancement
What is the origin of (anti-)proton enhancement
at intermediate pT?
PRL 91, 172301 (2003)
To distinguish the different production mechanism
for protons and pions at intermediate and higher
pT.
Possible sources (medium effect) - Strong
radial flow - Recombination - Baryon junction

• - p/? ratio 1 for central AuAu at intermediate
  pT (2-4 GeV/c).
• Larger than expected from fragmentation
  (measured in pp, ee-).
• Baryon / Meson difference at intermediate pT.
• (on RAA (nuclear modification factor) , v2
  (elliptic flow) etc.)

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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 p/K up to 8 GeV/c.
Drift Chamber (momentum meas.)
Tracking detectors (PC1,PC2,PC3)
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Data Analysis

• - Data set AuAu 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.

45 GeV/c
34 GeV/c
BG Subtraction
S/N12
S/N5
Using residual bending in ? direction.
67 GeV/c
56 GeV/c
Backgrounds - random association - electrons
from photon conversion - decayed products
S/N2
S/N1
track matching residual (a.u.)
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Results
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pT spectra of (anti-)protons
Work in Progress
pT reach extended for (anti-)protons with fine
centrality bins.
Work in Progress
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pbar/p vs. pT
Work in Progress
Peripheral
Central
Work in Progress
No significant centrality or pT dependence (up
to 6 GeV/c).
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p/? vs. pT
Work in Progress
p/?
No feed-down correction.
- p/? (pbar/?) 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/? vs. pT (centrality dep.)
Work in Progress
No feed-down correction.
p/?
Peripheral
Central
- p/? ratios look to have a peak at intermediate
pT (2-4 GeV/c). - Clear peak in central events
than that in peripheral.
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p/? vs. pT (centrality dep.)
Work in Progress
p/?
No feed-down correction. pp data
(nucl-ex/0603010)

• Centrality dependence seen in the magnitude.
• p/? ratio in peripheral lies slightly above the
  pp ratio.

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Comparison with Models
PRC 68, 044902 (2003)
PRC 69, 034908 (2004)
PRC 67, 034902 (2003)
p/?
PRL 90, 202302 (2003)
p/?

• Only look through several models (recombination,
  hydrojet, ).
• Novel mechanism of hadron production at
  intermediate pT.

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Summary

• pT reach of PID (especially for p, pbar)
  extended with
• (1) High statistics AuAu data
• (2) New PID detector (Aerogel)
• Results are still work-in-progress.
• pbar/p ratio
• - No centrality or pT dependence.
• p/? 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 pp (abundant) data to make RAA at
  higher pT.
• MRPC-TOF (?TOF100ps) to be installed for PID
  upgrade.

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Backup slides
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PID demonstration
No Cut
Aerogel Veto
p
K
p
Clear Proton Line !
- Mass square cut 2s 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.
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Charged pion spectra identified with ACC
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p/? ratio in CuCu / AuAu
Central AuAu
Central CuCu
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 AuAu (Npart scaling).

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RAA vs. pT
Npart98
Npart114
CuCu 200 GeV Central (0-10)
AuAu 200 GeV Mid-Central (30-40)
No feed-down correction.
- Similarity on RAA seen in CuCu and AuAu -
The magnitude of enhancement/suppression -
Particle type dependence
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Bump in the h/? ratios
PRC 69, 034910 (2004)

• Expectation (pp,ee-) 1.6
• Above 5 GeV/c and in peripheral
• events recover normal fragmentation.