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Diagnosing energy loss: PHENIX results on high-p T hadron spectra

Diagnosing energy loss: PHENIX results on high-p T hadron spectra. Baldo Sahlmüller, University of Münster for the PHENIX collaboration. A+A. p+p. Physics Motivation: Why high-p T ?. At high energy: hard scattering cross section large Measuring high p T particle yields:

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Diagnosing energy loss: PHENIX results on high-p T hadron spectra

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  1. Diagnosing energy loss: PHENIX results on high-pT hadron spectra Baldo Sahlmüller, University of Münster for the PHENIX collaboration

  2. A+A p+p Physics Motivation:Why high-pT? • At high energy: hard scattering cross section large • Measuring high pT particle yields: • Initial yields and pT distributions can be predicted from p+p measurements + pQCD + cold nuclear effects • Deviations can be attributed to the medium formed in A+A collisions • High pT particles (leading particles of jets) as h,p0 can be measured in large BGs (dNch/dh ~ 700) • Quantification with nuclear modification factor: Quark Matter 2006

  3. What we already know • System size dependence at 200 GeV • Suppression up to high pT • Consistent with dNg/dy = 1200 (Au+Au) and dNg/dy = 370 (Cu+Cu) • Similar suppression for similar Npart • Consistent with pure density and path • length dependence • also: taking into account shape • of nuclei Questions: What happens at lower energies? Connection towards SPS energies? Quark Matter 2006

  4. The PHENIX Experiment • Measurement of h, p0 via gg decay • Decay g’s are measured in EMCal • 2 sectors PbGl, 6 sectors PbSc in 2 arms • Covers |h|<0.35, f=180° • Granularity fine enough to measure p0’s up to pT ~ 25 GeV/c h, p0 Quark Matter 2006

  5. Diagnosing Heavy Ion Collisions So far: status of investigating energy loss with high pT particle production; dependence on: • Centrality OK • pTOK • System size (OK) => Next step: energy dependence Quark Matter 2006

  6. 200 GeV Quark Matter 2006

  7. T The p+p Reference • nucl-ex/0610036 h p0 • Measurement at 200 GeV => See poster by A. Bazilevsky! Quark Matter 2006

  8. nucl-ex/0610036 Initial State Effects? • New PHENIX paper on centrality dependence of p0+h in d+Au at 200 GeV • d+Au as collision system to look for initial state effects nucl-ex/0610036 => no strong initial state effects Quark Matter 2006

  9. Au+Au at 200 GeV • h data from RHIC run 2004 => See poster by M.L. Purschke! Quark Matter 2006

  10. RAA at 200 GeV • h in Au+Au => Suppression by a factor of 5 in central events Quark Matter 2006

  11. RAA at 200 GeV • Direct g, p0 and h in Au+Au • Direct g RAA with measured p+p reference! 0-10% central events • => RAA ofhandp0consistent, both show suppression • => RAA ofgis smaller than 1 at very high pT Quark Matter 2006

  12. 62.4 GeV Quark Matter 2006

  13. The p+p Reference • p+p parameterization at 62.4 GeV: Fit to existing (ISR) data at similar energies (D.d'Enterria. J.Phys.G31, S491 (2005)) Quark Matter 2006

  14. The p+p Reference • Problem: data sets inconsistent => large error • new important RHIC measurement in 2006 • Analysis still ongoing Quark Matter 2006

  15. Au+Au at 62.4 GeV • Au+Au p0: • Suppression in central events • Important: influence of error in p+p reference! • Theoretical curve: Vitev nucl-th/0404052 dNg/dy = 650-800 Quark Matter 2006

  16. Spectra in Cu+Cu at 62.4 GeV h p0 => See poster by T. Sakaguchi! Quark Matter 2006

  17. RAA in Cu+Cu at 62.4 GeV Cu+Cu p0: • centrality dependent • Important: Influence of error in p+p reference! • Centrality dependent behavior • Enhancement in peripheral events • RAA smaller in central events Quark Matter 2006

  18. RAA vs. Npart at 62.4 GeV • RAA integrated at high pT • Again: Large normalization uncertainty from p+p reference • RAA smaller towards higher Npart • Same theoretical model as for 200 GeV data consistent within errors Quark Matter 2006

  19. 22.4 GeV Quark Matter 2006

  20. The p+p Reference • p+p parameterization at 22.4 GeV: Fit to existing data at similar energies (D.d'Enterria. J.Phys.G31, S491 (2005)) Quark Matter 2006

  21. p0 at 22.4 GeV • Towards SPS energies: Cu+Cu at 22.4 GeV Little centrality dependence Quark Matter 2006

  22. SPS and RHIC • Same behavior for similar Npart (63 at WA98, 67.8 at PHENIX) Blattnig parameterization used for WA98 data (S. Blattnig et. al., Phys.Rev. D62 (2000) 094030 / D. D’Enterria, Phys. Lett. B 596 (2004) 32)) Quark Matter 2006

  23. RAA at Different Energies • Comparison of p0 in Cu+Cu at 200, 62.4, and 22.4 GeV • Measured the same collision species over a broad energy range • Suppression gets larger with higher energies Quark Matter 2006

  24. Particle Ratio Quark Matter 2006

  25. Ratio in Au+Au • Ratio h/p0 for different centralities in comparison with PYTHIA prediction PYTHIA works very well in describing the ratio in heavy-ion collisions Possible conclusion (for high pT): Suppression at partonic level, fragmentation outside medium Quark Matter 2006

  26. Ratio in p+p and Cu+Cu Cu+Cu • Ratio h/p0 • Approximately 0.5 at high pT • First PHENIX h measurement at 62.4 GeV nucl-ex/0611006 p+p Quark Matter 2006

  27. “World” data • All PHENIX data consistent with world data • Ratio shows no obvious energy dependence Quark Matter 2006

  28. Data vs. Theory? Quark Matter 2006

  29. Theory: Loizides, hep-ph/0608133v2 Comparing to Theories How probable is a certain parameter in theory? Taking into account errors of measurement (for a certain theory parameter): vary points within 4 RMS of correlated errors, find most probable point calculate probability for large number of randomly picked sets of correlated and uncorrelated errors see how many of these are worse than point from step 1 Quark Matter 2006

  30. Comparing to Theories another compilation… Theory: I. Vitev, Phys.Lett.B639:38-45,2006 Quark Matter 2006

  31. Comparing to Theories and another compilation… Theory: William Horowitz Quark Matter 2006

  32. Summary • Au+Au at 200 GeV • New h measurement up to pT = 15 GeV/c • Similar suppression patterns of h and p0 • Cu+Cu at 62.4 GeV • Strong p0 enhancement in peripheral events • RAA gets smaller in central events • Cu+Cu at 22 GeV • No significant centrality dependence in p0 production • Consistent with SPS results at 17.3 GeV • Ratio h/p0 • Ratio h/p0 similar for different collision systems and energies • Results in Cu+Cu and Au+Au consistent with partonic energy loss in the medium, fragmentation in the vacuum Quark Matter 2006

  33. Finally: Back to the List So far: status of investigating energy loss with high pT particle production; dependence on: • Centrality OK • pTOK • System size (OK) Quark Matter 2006

  34. Finally: Back to the List Now: status of investigating energy loss with high pT particle production; dependence on: • Centrality OK • pTOK • System size OK • Energy OK Quark Matter 2006

  35. 13 Countries; 62 Institutions; 550 Participants* *as of March 2005

  36. Related Talks and Posters • Talks • 2.2.5 V. S. Pantuev PHENIX measurements of reaction plane dependence of high-pT photons and pions in Au+Au collisions • 3.1.2 Yu. Riabov Measurement of leptonic and hadronic decays of w and f mesons at RHIC by PHENIX • 3.2.2 M. Konno High-pT Identified Hadron Production in Au+Au and Cu+Cu Collisions at RHIC-PHENIX • 3.3.1 T. Isobe Systematic Study of High-pT Direct Photon Production with the PHENIX Experiment at RHIC • Posters • 1.14 M. L. Purschke Measurement of h pT distributions in SNN =200 GeV Au-Au collisions at RHIC-PHENIX • 1.18 V. Ryabov Measurements of the multi-hadron decays of w and f mesons in heavy ion collisions at SNN= 200 GeV in the PHENIX experiment at RHIC • 2.38 M. Shimomura Measurement of Azimuthal Anisotropy for High-pT Charged Hadron at RHIC-PHENIX • 2.50 T. Sakaguchi System size and energy dependence of high-pT hadron production measured with the PHENIX experiment at RHIC • 2.51 D. Winter High-pT π0 production with respect to the reaction plane in SNN = 200 GeV Au+Au collisions at PHENIX Quark Matter 2006

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