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High-pT Direct Photon Spectra in 200GeV Au+Au Collisions at RHIC-PHENIX

This study presents measurements of direct photon spectra and azimuthal anisotropy in 200GeV Au+Au collisions at RHIC-PHENIX. Direct photons are essential probes of the initial hot and dense matter formed in heavy ion collisions. The analysis covers the production processes of photons, including jet fragmentation, hard scattered photons, and thermal radiation. The results demonstrate the production of high-pT direct photons in the initial stage, while thermal radiation is emitted in the low-pT region. The study also investigates the elliptic flow (v2) of emitted particles, reflecting the initial spatial anisotropy. The experimental setup of the PHENIX experiment and the inclusive photon analysis methods are detailed. Additionally, comparisons with theoretical predictions and discussions on the centrality dependence of direct photon v2 are presented.

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High-pT Direct Photon Spectra in 200GeV Au+Au Collisions at RHIC-PHENIX

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  1. High pT direct photon spectra and azimuthal anisotropy measurements in 200GeV Au+Au collisions at RHIC-PHENIX Quark-Matter 2008 20th International Conference on Nucleus Nucleus Collisions Kentaro MIKI (Univ. of Tsukuba) for the PHENIX collaboration mail to: kentaro@rcf2.rhic.bnl.gov 02/08/2008

  2. 1-1. Introduction ~Photons~ Photons are emitted from several stage of heavy ion collisions! sQGP Thermal Hadron decay Jet fragmentation Hard scattered Jet Brems. 1 QM 2008 - Kentaro Miki -

  3. 1-1. Introduction ~Photons~ Photons are emitted from several stage of heavy ion collisions! sQGP Thermal Hadron decay Jet fragmentation Hard scattered Jet Brems. Direct photons are not suppressed in Au+Au collisions. 1 QM 2008 - Kentaro Miki -

  4. 1-2. Introduction ~direct photon~ Direct photon is penetrating probe for initial hot and dense matter. There are many photon sources in heavy ion collisions. All NLO-pQCD QGP-Thermal Jet-photon Phys. Rev., C69:014903(2004) QM 2006 thermal window -> 1~3 GeV/c (?) prompt photon -> 6~ GeV/c (?) High pT direct photons are produced in the initial stage. Thermal radiation are emitted in the low pT region. 2 QM 2008 - Kentaro Miki -

  5. 1-3. Introduction ~v2~ The collision participation part in the early stage has spatial anisotropy. Pressure gradient is the largest in the shortest direction of the ellipsoid. Emitted particles reflect initial spatial anisotropy. -Elliptic flow (v2) is defined by the 2nd coefficient of Fourier expansion > S. Huang, (Parallel talk XII)  : azimuthal angle of particles  : azimuthal angle of reaction plane 3 QM 2008 - Kentaro Miki -

  6. 2-1. PHENIX experiment lead scintillator (PbSc) ・energy resolution 2.1  8.1 %/ E1/2 [GeV] || < 0.375 =902 lead glass (PbGl) ・energy resolution 0.76  5.95 %/ E1/2 [GeV] 4 QM 2008 - Kentaro Miki -

  7. Inclusive photon Direct  hadron decay 3-1. Analysis method ex. 0 invariant mass distribution 3.0 < pT < 4.0 0   ’ 5 QM 2008 - Kentaro Miki -

  8. Inclusive photon Direct  hadron decay 3-1. Analysis method 5 QM 2008 - Kentaro Miki -

  9. 3-2. Direct photon analysis ~spectra~ 200 GeV Run4 direct photon pT spectra (900M events) Reached up to 18GeV/c Direct photon spectra well described by NLO pQCD calculations. QM2006 proceeding T. Isobe 6 QM 2008 - Kentaro Miki -

  10. RAA with pQCD RAA with p+p data 3-2. Direct photon analysis ~spectra~ 200 GeV • Au+Au: Direct  RAAis equal to 1 below 14GeV/c. • (no suppress/enhance) • Direct  RAAis less than 1 above 14GeV/c. • ( Isospin effect? • EMC effect? • Suppression of fragmentation photons? ) K. Reygers (parallel session I) 6 QM 2008 - Kentaro Miki -

  11. RAA with pQCD RAA with p+p data 3-2. Direct photon analysis ~spectra~ 200 GeV Cu+Cu: Direct  RAAequal to 1 up to pT 17 GeV/c. Direct photon RAA in Cu+Cu supports simple TAB scaling of hard scattering up to highest pT Cu+Cu K. Reygers (parallel session I) 6 QM 2008 - Kentaro Miki -

  12. 3-3. Direct photon analysis ~spectra~ 62.4 GeV Run4 Au+Au 62.4 GeV direct photon spectra Direct photon at 62.4 GeV is also well described by NLO pQCD calculation above 5 GeV/c. sNN = 62.4 GeV, Au + Au 7 QM 2008 - Kentaro Miki -

  13. Inclusive photon Direct  Hadron decay hard scatter Jet Brems. Jet Fragment sQGP 4-1. Direct photon analysis ~v2~ The v2 is sensitive to the initial geometric overlap zone and pressure gradient. Therefore, direct photon v2 is considered to depend on the production processes of photons. 8 QM 2008 - Kentaro Miki -

  14. Inclusive photon Direct  Hadron decay hard scatter hard scatter v2 = 0 Jet Brems. Jet Brems. v2 < 0 Jet Fragment Jet Fragment v2 > 0 sQQP sQGP v2≥ 0 4-1. Direct photon analysis ~v2~ photons from jet annihilation compton scattering v2 > 0 Bremsstrahlung (energy loss) v2 < 0 8 QM 2008 - Kentaro Miki -

  15. 4-2. Run4 Result Direct photon v2 at 200GeV Au+Au (Run4) Above to 4GeV/c, equal to 0 ? In 3 to 4 GeV/c region is Non-zero v2 ?? Centrality dependence ??? 9 QM 2008 - Kentaro Miki -

  16. 4-3. Compared with predictions Rupa et al calculation Hydrodynamics with a thermalization at early times followed by hadronization and decoupling. PRL 96, 202302 (2006) > R. Chatterjee (poster 80) 10 QM 2008 - Kentaro Miki -

  17. 4-3. Compared with predictions Rupa et al calculation Tuibide et al calculation Hydrodynamic with a thermalization at early times followed by hadronization and decoupling. 2D+1 hydrodynamical model. Several different sources are considered. PRL 96, 202302 (2006) arXiv:0712.0732v2 > R. Chatterjee (poster 80) consistent to theoretical calculation … ? 10 QM 2008 - Kentaro Miki -

  18. 5-1. How to update? > Direct photon v2 in Run4 has large error bar 11 QM 2008 - Kentaro Miki -

  19. 5-1. How to update? > Direct photon v2 in Run4 has large error bar > Low pT region -- thermal photon from virtual gamma analysis > T. Dahms, (parallel talk XV) 11 QM 2008 - Kentaro Miki -

  20. 5-1. How to update? > Direct photon v2 in Run4 has large error bar > Low pT region -- thermal photon from virtual gamma analysis > T. Dahms, (parallel talk XV) > High pT region -- more statistics! -- Run 7 analysis -- improvement of event plane resolution! -- New detector 11 QM 2008 - Kentaro Miki -

  21. 5-2. Reaction plane detector (RXNP) Run7 has new detector for reaction plane definition. RXNP has twice better resolution than BBC. > Y. Ikeda, (poster 123) 12 QM 2008 - Kentaro Miki -

  22. 5-3. 0 v2 Run7 with RXNP 1.8 B events collected. Good agreement with Run4 Preliminary. Good accuracy up to 10 GeV/c. More data to analyze => up to 13 or 16 GeV/c > R. Wei, (poster 128) > Y. Aramaki, (poster 143) 13 QM 2008 - Kentaro Miki -

  23. 5-4. compared with … … with inclusive photon v2 (Run 4) We can see the same (or less) statistical uncertainty even inclusive photon. Run7 allows us more detail comparison between hadron decay photon and inclusive photon. 14 QM 2008 - Kentaro Miki -

  24. 5-4. compared with … … with inclusive photon v2 (Run 4) … with charged hadron v2 (Run 7) We can see the same (or less) statistical uncertainty even inclusive photon. Run7 allows us more detail comparison between hadron decay photon and inclusive photon. Good agreement to charged pion v2. > S. Huang, (parallel talk XII) 14 QM 2008 - Kentaro Miki -

  25. 6. Summary 1. Direct photon is one of the interesting measurement as penetrating probe for initial hot and dense matter. 2. The photon excess ratio is measured in 200 GeV and 62.4 GeV. 3. The invariant yield is well described by NLO pQCD. 4. Direct photon v2 is measured in Run4, with large error bar. => consistent with theoretical prediction in high pT. 5. Run7 0 v2 is measured as a function of pT. => Run7 allows us more detail direct photon study at high pT in a near future. 6. Thank you for all collaborators! 15 QM 2008 - Kentaro Miki -

  26. Ex Back up QM 2008 - Kentaro Miki -

  27. Ex. In the 2~4 GeV/c region, 1. Enhancement of direct photon in Au+Au 2. Direct photon v2 might be non-zero => There is other components ?? QM 2008 - Kentaro Miki -

  28. Ex. Decay photon and inc. photon (run 4) 0 v2 as EXODUS input 0 v2 from latest Dave’s analysis. In order to define the EXODUS input, fitting 1 function below 4GeV/c and fitting point to point above 4GeV/c. decay photon and inc. photon v2 Generated decay photon v2 by Monte Carlo. Error bar is propagated from 0 sta. and sys. error to decay photon as sys. error. In this plot, assumed the KET scaling for , ,  and ’. QM 2008 - Kentaro Miki -

  29. Ex. pi0 v2 in Run4 QM 2008 - Kentaro Miki -

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