konno qm2006 final version

Slide1: 

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

Slide2: 

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

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Physics Motivation 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. Au+Au 200 GeV - Baryon Enhancement - RAA

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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. Time of Flight (TOF) Veto for proton ID π+ K+ p Aerogel Cherenkov (ACC)

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

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pT 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.

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p/ vs. pT 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)) Au+Au 200 GeV ACC

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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. ACC p/ vs. pT Cu+Cu 200 GeV p/

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p/ vs. Npart1/3 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) 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.

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p/ vs. pT (Low pT) 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. - Radial flow -

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

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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. - Quark Recombination - At intermediate pT, recombination of partons may be a more efficient mechanism of hadron production than fragmentation. p/ vs. pT (Intermediate pT) NOTE: No weak decay feed-down correction applied. ACC

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

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

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p/ vs. Npart1/3 ,(dET/dy)1/3 Au+Au 200 GeV vs. Au+Au 62 GeV 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. TOF

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RAA vs. pT 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

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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.