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Direct Photons in 200 GeV p+p , d +Au, Au+Au

Direct Photons in 200 GeV p+p , d +Au, Au+Au. Stefan Bathe UC Riverside for the PHENIX collaboration. QM 2005, Budapest, August 4-9. p+p : Test of QCD Reduce uncertainty on pQCD photons in A+A

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Direct Photons in 200 GeV p+p , d +Au, Au+Au

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  1. Direct Photons in 200 GeV p+p, d+Au, Au+Au Stefan Bathe UC Riverside for the PHENIX collaboration QM 2005, Budapest, August 4-9

  2. p+p: Test of QCD Reduce uncertainty on pQCD photons in A+A d+Au Study nuclear effects Why Direct Photons? • A+A • Photons don’t strongly interact with produced medium • Hard photons • Allow test of Ncoll scaling for hard processes • Important for interpretation of high-pT hadron suppression at RHIC • Thermal photons • Carry information about early stage of collision • QGP potentially detectable via thermal photon radiation Stefan Bathe

  3. Hard Photons p+p Stefan Bathe

  4. good agreement with NLO pQCD Important baseline for Au+Au New for QM: PHENIX Preliminary Poster O. Zaudtke PbSc PbSc PbGl new Poster A. Hadj Henni Direct Photons in p+p Stefan Bathe

  5. Hard Photons d+Au Stefan Bathe

  6. p+p and d+Au spectra compared to NLO pQCD Direct g in d+Au • ratio to NLO pQCD • consistent with 1 • No indication for nuclear effects 2 Poster H. Torii Poster D. Peressounko Stefan Bathe

  7. Hard Photons Au+Au Stefan Bathe

  8. Direct Photons in Au+Au p0 suppression caused by medium created in Au+Au collisions Recentlypublished PRL 94, 232301 Expectation for Ncoll scaling of direct photons holds for all centrality classes Stefan Bathe

  9. Thermal Photons Au+Au Stefan Bathe

  10. thermal: Decay photons hard: Schematic Photon Spectrum in Au+Au Stefan Bathe

  11. Going to low pT • No significant excess at low pT Stefan Bathe

  12. Poster T. Sakaguchi New from Run4 • New data set • Selection of most stable runs • Re-evaluation of systematic uncertainties • Stay tuned for more improvements Stefan Bathe

  13. Thermal Photons Au+Au A New Approach Stefan Bathe

  14. direct photon analysis new dilepton analysis conventional dilepton analysis Opening up the phase space pT Minv 0 Stefan Bathe

  15. e+ Compton e- g* q g g g q p0 p0 e+ g* g e- Compton g q g q The Idea • Start from Dalitz decay • Calculate invariant mass distribution of Dalitz pairs invariant mass of Dalitz pair invariant mass of Dalitz pair invariant mass of virtual photon invariant mass of virtual photon form factor form factor phase space factor phase space factor • Now direct photons • Any source of real g produces virtual gwith very low mass • Rate and mass distribution given by same formula • No phase space factor for mee<< pT photon Stefan Bathe

  16. Method • Material conversion pairs removed by analysis cut • Combinatorics removed by mixed events 0-30 90-140 200-300 140-200 MeV Rdata ÷ ÷ ÷ • Calculate ratios of various Minv bins to lowest one: Rdata • If no direct photons: ratios correspond to Dalitz decays • If excess:direct photons Stefan Bathe

  17. Stefan Bathe

  18. g h p0 Stefan Bathe

  19. g g h h p0 S/B=~1 p0 Stefan Bathe

  20. Rdirect g g h h Rh p0 Rp0 ÷ Rdata S/B=~1 calculated from Dalitz formula p0 measured Stefan Bathe

  21. Rdirect g g h h Rh p0 Rp0 ÷ Rdata S/B=~1 calculated from Dalitz formula p0 measured Stefan Bathe

  22. ~25 % systematic error : ~20 % from measured h/p0 ratio ~10 % from g inclusive ~5 % acceptance Rdirect g g h h Rh p0 Here we are… Rp0 measured with EMCal ÷ Rdata S/B=~1 calculated from Dalitz formula p0 measured Stefan Bathe

  23. Rdata 140-200 MeV 0-20 % Stefan Bathe

  24. g*direct/g*inclusive 0-20 % Significant 10% excess of very-low-mass virtual direct photons Stefan Bathe

  25. more peripheral Centrality Dependence Indication for centrality dependence Stefan Bathe

  26. ( + 1 ) Comparison to Conventional result Stefan Bathe

  27. gdirect Stefan Bathe

  28. The Spectrum Compare to published Run2 result: PRL94 232301 Stefan Bathe

  29. Compare to NLO pQCD • L.E.Gordon and W. Vogelsang • Phys. Rev. D48, 3136 (1993) • excess above pQCD The Spectrum Stefan Bathe

  30. Compare to NLO pQCD • L.E.Gordon and W. Vogelsang • Phys. Rev. D48, 3136 (1993) • excess above pQCD The Spectrum Compare to thermal model • D. d’Enterria, D. Perresounko • nucl-th/0503054 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c • data above thermal at high pT Stefan Bathe

  31. Compare to NLO pQCD • L.E.Gordon and W. Vogelsang • Phys. Rev. D48, 3136 (1993) • excess above pQCD The Spectrum Compare to thermal model • D. d’Enterria, D. Perresounko • nucl-th/0503054 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c • data above thermal at high pT Compare to thermal + pQCD • data consistent with thermal + pQCD Stefan Bathe

  32. Conclusions • Thermal (?) direct photons 1<pT<4GeV/c • New EMCal measurement with reduced systematics • Stay tuned for further improvements • New measurement through very-low-mass virtual photons • Significant 10% direct photon excess above decay photons • Spectrum consistent with thermal model • Hard direct photons pT>4GeV/c • p+p: • Spectrum consistent with pQCD calculations • d+Au: • No apparent nuclear effects • Au+Au: • Confirms Ncoll scaling for hard processes Stefan Bathe

  33. Stefan Bathe

  34. Backup Stefan Bathe

  35. Stefan Bathe

  36. QGP + HG rates convoluted with simple fireball model plus pQCD hard photons Data described with initial temperature Ti=205 MeV + some nuclear kT broadening (Cronin-effect) Data also described without kT broadening but with high initial temperature (Ti=270 MeV) WA98 Interpretation: T or kT ? Turbide, Rapp, Gale, Phys. Rev. C 69 (014902), 2004 Stefan Bathe

  37. Turbide, Rapp, Gale (Phys.Rev.C69:014903,2004 ) QGP + HG + pQCD with kT Ti = 205 MeV, t0 = 1 fm/c QGP + HG + pQCD without kT Ti = 250 - 270 MeV, t0 = 0,5 fm/c Renk (Phys.Rev.C67:064901,2003) QGP + HG + pQCD 250 < Ti < 370 MeV,0,5 < t0 < 3 fm/c Svrivastava (nucl-th/0411041) QGP + HG + pQCC(Bjorken hydro) Ti = 335 MeV, t0 = 0,2 fm/c Huovinen, Ruuskanen, Räsänen (Nucl. Phys. A 650 (227) 1999) QGP + HG + pQCD(Non-boost inv. hydro) Ti = 214 - 255 MeV Pure HG + pQCD(Non-boost inv. hydro) Ti = 213 - 234 MeV WA98 Data: Conclusions • Data consistent with QGP picture, but also with pure HG picture • Large variations in extracted initial temperature Ti(however, most models give Ti > Tc) Data can be described under a variety of different assumptions, e.g.: Stefan Bathe

  38. PHENIX p0RdA--Final Cronin effect small! New for QM: to be published Stefan Bathe

  39. Stefan Bathe

  40. 90-140 90-140 MeV, 20-40 % Stefan Bathe

  41. Only Ncoll scaling? • What about fragmentation photons? • fragmentation contribution substantial in p+p • parton energy loss in QGP reduces fragmentation contribution in Au+Au • compensated by induced photon bremsstrahlung in QGP fragmentation contribution (%) • Effects cancel? Stefan Bathe

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