High pt Hadrons from  sNN = 130 GeV Au-Au collisions measured in PHENIX

1. High pt Hadrons from sNN = 130 GeV Au-Au collisions measured in PHENIX Julia Velkovska (BNL) for PHENIX • High pT measurements in PHENIX • Identified protons and anti-protons – 3.5 GeV/c • Neutral pion analysis – up to 4 GeV/c • Charged hadron analysis - up to 5 GeV/c • Results • Transverse momentum spectra (identified charged hadrons) • <pT> and dN/dy as a function of Npart • Combine with p0 measurement - > ratios at high pT for 10% central • Decomposition of the charged hadron spectra to mesons and baryons • Conclusions and outlook High PT Workshop, BNL Julia Velkovska

2. Identified charged hadrons Tracking system: Drift Chamber , PC1 dp/p = 0.6% + 3.5% p (GeV/c) Timing system: BBC - start TOF - stop s = 115 ps Acceptance: D f = 45 deg D h = 0.7 PID : momentum dependent bands in mass2 High PT Workshop, BNL Julia Velkovska

3. Neutral pion measurement Two analyses with very different systematics • pair measurement (yields from invariant mass distributions) • yields extracted statistically – large combinatorial background • requires many events • difficult at low pT • signal to background improves at higher pT PbSc PbGl High PT Workshop, BNL Julia Velkovska

4. Charged hadrons • single particles, no combinatorial background • better per-event statistics, need fewer events for same pT range • momentum reconstruction increasingly difficult with higher pT Drift Chamber PC1: tracking PC3 - used to cut background High PT Workshop, BNL Julia Velkovska

5. Zero Degree Calorimeters (ZDC) Sensitive to spectator neutrons Using a combination of the ZDC’s and BBC’s we can define Centrality Classes 0 - 5 % Measuring Collision Centrality ZDC 5 - 10 % BBC High PT Workshop, BNL Julia Velkovska

6. Identified charged hadron spectra Central peripheral mid - central High PT Workshop, BNL Julia Velkovska

7. Hydro + cascade or baryon junctions + pQCD ? Hydro+cascade D. Teaney et.al. 5% central Baryon junctions + pQCD I.Vitev et.al. Both theories can describe the data up to 3 GeV/c High PT Workshop, BNL Julia Velkovska

8. Mean transverse momentum • Mean pt growing with Npart and mass - consistent fith flow • (Anti)proton <pT> significant increase from pp collisions • The same relative increase from peripheral to central for all particles 20+/- 5 % increase 20+/- 5 % increase High PT Workshop, BNL Julia Velkovska

9. Yields as a function of Npart • Is the increase in dNch/dh / (0.5 Np)due to hard processes ? • How does the yield per participant behave for different particles ? High PT Workshop, BNL Julia Velkovska

10. Identified charged hadron yields • Anti-proton and proton yields per participant pair rise faster than pion yields with Npart ! • Different from SPS Pb-Pb 20 +/- 6% increase 65 +/- 7 % increase High PT Workshop, BNL Julia Velkovska

11. Identified hadron spectra in central Au-Au collisions Excellent agreement between charged and neutral pions ! (anti)proton – pion crossing confirmed! High PT Workshop, BNL Julia Velkovska

12. Nucleon to Pion Ratios p/p+and p/p0rising with pT p/p-and p/p0rising or saturating at high pT Different from pp collisions - (anti)protons don’t come from jets High PT Workshop, BNL Julia Velkovska

13. Anti-proton /proton ratio in Central Au-Au Collisions flat or falling? Not enough statistics in year 2000 run PHENIX has x 10 more statistics on tape from year 2001 run High PT Workshop, BNL Julia Velkovska

14. Theory expectations: pQCD++ • p/p ratio falling with pT • Jet quenching moves the p/p ratio below the pp value • PHENIX will measure pp collisions this year • p/p ratio has a peak which changes with centrality hydrodynamics • p/p ratio flat with pT • p/p ratio steadily rising with pT High PT Workshop, BNL Julia Velkovska

15. High density QCD expects mT scaling : The data are consistent with mT scaling up to 3.5 GeV. High PT Workshop, BNL Julia Velkovska

16. Hadron suppression at high pT high pT hadron suppression different suppression for h and p0 High PT Workshop, BNL Julia Velkovska

17. Decomposing the hadron spectra to mesons and nucleons • Subtract anti-protons and protons from charged hadrons • Compare the meson spectrum to p0 Difference in high pT charged hadron And p0 suppression primarily due to nucleons High PT Workshop, BNL Julia Velkovska

18. We can measure it - can you predict it for sNN = 200 GeV Au-Au collisions ? • (Anti)proton / pion ratio as a function of pT for different centralities • anti-proton / proton ratio as a function of pT for different centralities • <pT> as a function of Npart and mass • dN/dy as a function of Npart and mass • High pT suppression for mesons and baryons • All these taken together can help differentiate between different production mechanisms at high pT High PT Workshop, BNL Julia Velkovska

19. Conclusions • PHENIX measured p,p,p0,h up to 3.5,4,5 GeV/c • All measurements are internally consistent • Protons dominate over pions at high pt in central collisions • Mean pT increases with Npart similarly for all particle species • dN/dy per participant pair rises faster for (anti)protons than for pions • p/p ratio rising with pt , approaching 1 and suggestive for saturating behavior – more statistics needed • p/p ratio flat or falling at high pt - inconclusive due to low statistics • Hadron suppression at high pt • Different high pt behavior for mesons and baryons High PT Workshop, BNL Julia Velkovska

20. Outlook - Year 2 Run Present run started July 2001 Hope to collect: ~ 300 mb-1 Au + Au ~ 3.5 pb-1 p + p Will be able to pin down the high pT behavior of p-/p and p-/p ratios both in Au-Au and pp New detectors: • 8 complete sectors of EMCAL (6 PbSc, 2 PbGl) • Rebuilt drift chamber • Multiplicity vertex detector (MVD) • South Muon Spectrometer • Upgraded trigger • Upgraded data aquisition High PT Workshop, BNL Julia Velkovska