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

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

Physics Motivation - Baryon Enhancement - RAA p/ ratio Au+Au 200 GeV PRC 74, 024904 (2006) PRL 91, 172301 (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.

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

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.

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.

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, 024904 (2006))

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.

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 3.0 - 4.0 GeV/c 4.0 - 5.0 GeV/c 2.0 - 3.0 GeV/c 0.6 - 1.5 GeV/c 1.0 - 2.0 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.

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.

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

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) 044902 Greco, V et al PRL 90 (2003) 202302 Hwa, R et al PRC 70(2004) 024905 etc. NOTE: No weak decay feed-down correction applied.

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.

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.

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.

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 1.5 - 4 GeV/c for all centralities. (enhancement > suppression) - Suppression is seen for pions, kaons. NOTE: No weak decay feed-down correction applied.

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.