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Neutral Pions in 200 GeV Cu+Cu Collisions

Neutral Pions in 200 GeV Cu+Cu Collisions. Stefan Bathe UC Riverside for the PHENIX Collaboration. DNP/JPS 2005, Maui, September 20. no effect. Hard Scattering and R AA. Hard processes yield scales with N coll small cross section incoherent superposition

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Neutral Pions in 200 GeV Cu+Cu Collisions

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  1. Neutral Pions in 200 GeV Cu+Cu Collisions Stefan BatheUC Riversidefor the PHENIX Collaboration DNP/JPS 2005, Maui, September 20 Stefan Bathe

  2. no effect Hard Scattering and RAA • Hard processes • yield scales with Ncoll • small cross section • incoherent superposition • Nuclear Modification Factor RAA strong suppression • absence of nuclear effects: RAA=1 at high pT • Strong suppression in central Au+Au Phys.Rev.Lett.91:072301,2003 Stefan Bathe

  3. Cause for Suppression Phys.Rev.Lett.91:072303 • Initial- or final-state effect? • Non-suppression in d+Au • Non-suppression of direct photons in Au+Au • final-state effect • To learn more • study system-size dependence Phys.Rev.Lett.94:232301,2005 Stefan Bathe

  4. System-Size Dependence • Vary centrality • Vary nucleus size • different geometrical shape • more precise centrality determination for small systems Au+Au Cu+Cu Stefan Bathe

  5. 60-80% 50-60% 30-40% centrality 80-92.2% Au+Au A=197 6.3 19.5 45.5 114 <Npart> 6.4 25.4 53.0 98.2 Cu+Cu A=64 40-50% 20-30% 0-10% 60-94% centrality Npart(x,y) Transverse Npart density for similar <Npart> in Au+Au and Cu+Cu ellipticity different Stefan Bathe

  6. Central spectrometer arms |h| < 0.35 g, and p0,h via 2-g decay Electromagnetic calorimeter (EMCal) Lead scintillator calorimeter (PbSc) Lead glass calorimeter (PbGl)  p0  PHENIX Experimental Setup Stefan Bathe

  7. 0Spectra in 200 GeV Cu+Cu • 56 M minimum-bias events • 1.9 M high-pT events recorded, 2.2 B sampled • pT range 1-17 GeV/c • Also measured 62.4 GeV and 22.5 GeV • need p+p reference Stefan Bathe

  8. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  9. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  10. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  11. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  12. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  13. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  14. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  15. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions Stefan Bathe

  16. 0RAA in 200 GeV Cu+Cu • RAA ~ 1 in peripheral collisions • RAA ~ 0.4 for central collisions Stefan Bathe

  17. 0RAA in 200 GeV Cu+Cu Charged hadrons: see Carla Vale’s talk, BF11 • RAA ~ 1 in peripheral collisions • RAA ~ 0.4 for central collisions • Charged-hadron RAA larger in central collisions Stefan Bathe

  18. Similar behavior for Au+Au and Cu+Cu for same Npart Comparing Au+Au and Cu+Cu Suppression 2x stronger in central Au+Au, but: p0 p0 p0 Stefan Bathe

  19. Model Comparison • Models • parton energy loss through gluon radiation • density and path-length dependend • Models describe data well Dainese, C. Loizides, G. Paic, Eur.Phys.J.C38:461,2005 X. N. Wang, Phys.Lett.B595:165,2004 I. Vitev, Phys.Rev.Lett.89:252301,2002 Stefan Bathe

  20. Model Comparison V. Pantuev, hep-ph/0506095, corona jet production density and path-length dependend Stefan Bathe

  21. Corona Jet Production V. Pantuev, hep-ph/0506095 • Different surface-to-volume ratio, different absorption for same Npart Stefan Bathe

  22. Summary and Outlook • High-pT0(h+-) suppression in central Cu+Cu at 200 GeV • Suppression similar to that in Au+Au for same Npart • Consistent with pure density and path-length dependence • Hints for shape-dependent suppression mechanism for same system size • More information from reaction-plane dependence Stefan Bathe

  23. Stefan Bathe

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