1. High-pT Identified Hadron Production in Au+Au and Cu+Cu Collisions
at RHIC-PHENIX
Masahiro Konno
(Univ. of Tsukuba)
for the PHENIX Collaboration

2. Outline Physics Motivation Method
New Data Set (full statistics now available) :
Cu+Cu 200GeV / p+p 200 GeV
Results and Comparisons:
- p/ ratios
- Npart Scaling of p/ in Au+Au, Cu+Cu
- RAA in Au+Au, Cu+Cu
Summary

3. Physics Motivation - Baryon Enhancement - RAA p/ ratio Au+Au 200 GeV
PRC 74, (2006)
PRL 91, (2003)
p/ ratio
Au+Au 200 GeV
What is the origin of (anti-)proton
enhancement at intermediate pT(2~5 GeV/c) ?
A systematic study at intermediate pT is
necessary over different collisions systems.
High-pT suppression due to parton energy loss
in the medium (jet quenching).
The suppression patterns depend on particle type.
Protons are enhanced, while pions and kaons are suppressed.

4. PHENIX detector - - EM Calorimeter (PID) TOF (PID)
- Central Arm Detectors
(magnetic spectrometer)
Event Characterization detectors
PID (particle identification) is
a powerful tool to study hadron
production.
Aerogel Cherenkov (PID)
Aerogel Cherenkov (ACC)
Time of Flight (TOF)
p (p) ID up to 7 GeV/c -
p (p) ID up to 4 GeV/c -
Drift Chamber
(momentum meas.) p K+
Tracking detectors
(PC1,PC2,PC3) π+
Veto for proton ID

5. pT spectra (Cu+Cu √sNN = 200 GeV)
Phenix preliminary
(Anti-) protons
ACC
pT reach extended for (anti-)protons with fine centrality bins.
<= (1) Aerogel Cherenkov, (2) Enough statistics in Au+Au/Cu+Cu
NOTE: No weak decay feed-down correction applied.

6. pT spectra (p+p √s = 200 GeV)
Phenix preliminary
TOF
High statistics 200 GeV p+p data.
More than10 times statistics used compared to previous Run3 p+p analysis.
The p+p data provides baseline spectra to heavy ion data, and it is
important to quantify in-medium nuclear effects in heavy ion collisions at RHIC.
NOTE: No weak decay feed-down correction applied.

7. p/ vs. pT Au+Au 200 GeV ACC p/ p/
- p/ (pbar/) ratios seem to turn over at intermediate pT,
and be close to the value of fragmentation at higher pT.
- Clear peak in central events than that in peripheral.
- Indicating a transition from soft to hard at intermediate pT.
NOTE: - No weak decay feed-down correction applied.
- p+p data (PRC 74, (2006))

8. p/ vs. pT Cu+Cu 200 GeV ACC p/ p/
Phenix preliminary
p/
p/
Baryon enhancement observed in Cu+Cu at 200 GeV.
- pT dependence in Cu+Cu is similar to that in Au+Au.
=> How about the magnitude as a function of centrality? see Next.
NOTE: No weak decay feed-down correction applied.

9. p/ vs. Npart1/3 3.0 - 4.0 GeV/c 4.0 - 5.0 GeV/c 2.0 - 3.0 GeV/c
Cu+Cu 200 GeV
vs. Au+Au 200 GeV
p/ vs. Npart1/3 pT
Phenix preliminary
GeV/c
GeV/c
GeV/c
GeV/c
GeV/c
Phenix
preliminary
Centrality dependence in Cu+Cu looks similar to
that in Au+Au (Npart scaling at same sqrt(sNN)!).
- Even though overlap region has a different geometrical shape.
- Slight difference in the magnitude seen.
TOF (<3 GeV/c)
ACC (>3 GeV/c)
NOTE: No weak decay
feed-down correction
applied.

10. p/ vs. pT (Low pT) - Radial flow - TOF (Anti-)protons
Phenix preliminary
Phenix preliminary
At low pT, p/ shows weak and decreasing Npart dependence because inverse slope (from mT exponential fitting) also shows it.
NOTE: No weak decay feed-down correction applied.

11. p/ vs. pT (Intermediate pT)
TOF, ACC
- Radial flow (ex. blast-wave fit) -
Au+Au 200 GeV
Spectra for heavier particles has
a convex shape due to radial flow.
Using Blast-wave fitting, try to
estimate p/ ratio as a function of pT.
NOTE: No weak decay feed-down correction applied.
(hydro p)/(hydro )
(hydro p)/(real )
Hydrodynamic contribution for protons is one of
the explanations (baryon enhancement).
- Other contribution is also needed: Recombination, Jet fragmentation
Central
Peripheral

12. p/ vs. pT (Intermediate pT)
ACC
- Quark Recombination -
p/
Phenix preliminary
Now, we find a similar trend.
ACC
TOF
At intermediate pT, recombination of
partons may be a more efficient mechanism
of hadron production than fragmentation.
A number of models predicted a turnover
in the B/M ratio at pT just above where
the available data finished…
Fries, R et al PRC 68 (2003)
Greco, V et al PRL 90 (2003)
Hwa, R et al PRC 70(2004) etc.
NOTE: No weak decay feed-down correction applied.

13. p/ vs. pT Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary
- Again, look at centrality dependence of p/ ratios.
- Similar tendencies as at 200 GeV.

14. p/ vs. Npart1/3 Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary
Npart scaling of p/ also at 62 GeV in Au+Au/Cu+Cu.
NOTE: No weak decay feed-down correction applied.

15. p/ vs. Npart1/3 ,(dET/dy)1/3
Au+Au 200 GeV
vs. Au+Au 62 GeV
TOF
Phenix preliminary
Phenix preliminary
No Npart scaling of p/ (pbar/) in Au+Au between 62 GeV and 200 GeV.
dET/dy scaling of pbar/ seen. => Proton production (this pT range)
at 62 GeV is partly from baryon transport, not only pair production.
Nuclear stopping is still large at 62 GeV.
NOTE: No weak decay feed-down correction applied.

16. RAA vs. pT TOF Phenix preliminary Similar Npart dependence
NOTE: Systematic errors (~10%)
for overall normalization not shown.
Similar Npart dependence
for Au+Au / Cu+Cu.
(Npart scaling of RAA)
- Cronin effect in peripheral
Proton, antiproton are enhanced at GeV/c
for all centralities. (enhancement > suppression)
- Suppression is seen for pions, kaons.
NOTE: No weak decay feed-down correction applied.

17. Summary pT reach of PID (especially for p, pbar) extended with:
(1) High statistics Au+Au/Cu+Cu data
(2) New PID detector (Aerogel)
(Anti-)Proton enhancement is observed
in Au+Au/Cu+Cu collisions at 200/62 GeV.
p/ ratios:
(1) Indicating a transition from soft to hard production at intermediate pT.
(2) Npart scaling (dET/dy scaling) over different collision systems.
(3) Recombination + radial flow would explain the pT, Npart dependencies.
- Systematic study of PID spectra (and jet correlations)
for different collision systems can provide information
to understand the hadron production mechanisms.