1. QM2006 Shanghai, China 1 High-p T Identified Hadron Production in Au+Au and Cu+Cu Collisions at RHIC-PHENIX Masahiro Konno (Univ. of Tsukuba) for the PHENIX Collaboration

2. QM2006 Shanghai, China 2 Outline - Physics Motivation - Method - New Data Set (full statistics now available) : Cu+Cu 200GeV / p+p 200 GeV - Results and Comparisons: - p/  ratios - N part Scaling of p/  in Au+Au, Cu+Cu - R AA in Au+Au, Cu+Cu - Summary

3. QM2006 Shanghai, China 3 Physics Motivation - High-p T 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. Au+Au 200 GeV - Baryon Enhancement - PRL 91, 172301 (2003) p/  ratio PRC 74, 024904 (2006) - What is the origin of (anti-)proton enhancement at intermediate p T (2~5 GeV/c) ? - A systematic study at intermediate p T is necessary over different collisions systems. R AA

4. QM2006 Shanghai, China 4 PHENIX detector Aerogel Cherenkov (PID) EM Calorimeter (PID) TOF (PID) Drift Chamber (momentum meas.) Tracking detectors (PC1,PC2,PC3) - Central Arm Detectors (magnetic spectrometer) - Event Characterization detectors - PID (particle identification) is a powerful tool to study hadron production. p (p) ID up to 7 GeV/c - p (p) ID up to 4 GeV/c - Time of Flight (TOF) Veto for proton ID π+π+ K+K+ p Aerogel Cherenkov (ACC)

5. QM2006 Shanghai, China 5 p T spectra (Cu+Cu √s NN = 200 GeV) NOTE: No weak decay feed-down correction applied. Phenix preliminary - p T reach extended for (anti-)protons with fine centrality bins. <= (1) Aerogel Cherenkov, (2) Enough statistics in Au+Au/Cu+Cu (Anti-) protons ACC

6. QM2006 Shanghai, China 6 p T spectra (p+p √s = 200 GeV) - 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. Phenix preliminary TOF

7. QM2006 Shanghai, China 7 p/  vs. p T p/  - p/  (pbar/  ) ratios seem to turn over at intermediate p T, and be close to the value of fragmentation at higher p T. - Clear peak in central events than that in peripheral. - Indicating a transition from soft to hard at intermediate p T. NOTE: - No weak decay feed-down correction applied. - p+p data (PRC 74, 024904 (2006)) Au+Au 200 GeV ACC

8. QM2006 Shanghai, China 8 - Baryon enhancement observed in Cu+Cu at 200 GeV. - p T 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. Phenix preliminary ACC p/  vs. p T Cu+Cu 200 GeV p/ 

9. QM2006 Shanghai, China 9 p/  vs. N part 1/3 Phenix preliminary Cu+Cu 200 GeV vs. Au+Au 200 GeV NOTE: No weak decay feed-down correction applied. TOF (<3 GeV/c) ACC (>3 GeV/c) 0.6 - 1.5 GeV/c1.0 - 2.0 GeV/c2.0 - 3.0 GeV/c3.0 - 4.0 GeV/c4.0 - 5.0 GeV/c pTpT pTpT Phenix preliminary N part dependence in Cu+Cu looks similar to that in Au+Au (N part scaling !). Slight difference in the magnitude seen.

10. QM2006 Shanghai, China 10 p/  vs. p T (Low p T ) At low p T, p/  shows weak and decreasing N part dependence because inverse slope (from m T exponential fitting) also shows it. NOTE: No weak decay feed-down correction applied. - Radial flow - (Anti-)protons TOF Phenix preliminary

11. QM2006 Shanghai, China 11 - Radial flow (ex. blast-wave fit) - p/  vs. p T (Intermediate p T ) 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 p T. (hydro p)/(hydro  ) (hydro p)/(real  ) NOTE: No weak decay feed-down correction applied. TOF, ACC CentralPeripheral - Hydrodynamic contribution for protons is one of the explanations (baryon enhancement). - Other contribution is also needed: Recombination, Jet fragmentation

12. QM2006 Shanghai, China 12 A number of models predicted a turnover in the B/M ratio at p T just above where the available data finished… Fries, R et al PRC 68 (2003) 044902 Greco, V et al PRL 90 (2003) 202302 Hwa, R et al PRC 70(2004) 024905 etc. - Quark Recombination - At intermediate p T, recombination of partons may be a more efficient mechanism of hadron production than fragmentation. p/  vs. p T (Intermediate p T ) NOTE: No weak decay feed-down correction applied. ACC p/  Phenix preliminary Now, we find a similar trend. ACCTOF

13. QM2006 Shanghai, China 13 - Similar tendencies as at 200 GeV. p/  vs. p T Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary

14. QM2006 Shanghai, China 14 p/  vs. N part 1/3 Cu+Cu 62 GeV vs. Au+Au 62 GeV - N part scaling of p/  also at 62 GeV in Au+Au/Cu+Cu. Phenix preliminary NOTE: No weak decay feed-down correction applied. TOF

15. QM2006 Shanghai, China 15 p/  vs. N part 1/3, (dE T /dy) 1/3 Au+Au 200 GeV vs. Au+Au 62 GeV - No N part scaling of p/  (pbar/  ) in Au+Au between 62 GeV and 200 GeV. - dE T /dy scaling of pbar/  seen. => Proton production (this p T range) at 62 GeV is partly from baryon transport, not only pair production. NOTE: No weak decay feed-down correction applied. TOF Phenix preliminary

16. QM2006 Shanghai, China 16 R AA vs. p T - Proton, antiproton are enhanced at 1.5 - 4 GeV/c for all centralities. (enhancement > suppression) - Suppression is seen for pions, kaons. NOTE: No weak decay feed-down correction applied. TOF Phenix preliminary NOTE: Systematic errors (~10%) for overall normalization not shown. - Similar N part dependence for Au+Au / Cu+Cu. - Cronin effect in peripheral

17. QM2006 Shanghai, China 17 Summary - p T 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 p T. (2) N part scaling (dE T /dy scaling) over different collision systems. (3) Recombinatio + radial flow would explain the p T, N part dependencies. - Systematic study of PID spectra (and jet correlations) for different collision systems can provide information to understand the hadron production mechanisms.