Photon radiation from heavy ion collisions --Early Stage

1. Photon radiation from heavy ion collisions --Early Stage Outline Fu-Ming LIU （刘复明） • Motivations • Approach • Results • Conclusions Thermal Photons and Dileptons， BNL， August 20-22

2. Our brilliant universe • Photons carry us most information of our universe to us ! • To understand the puzzles of our universe, we should • understand photons from heavy ion collisions first.

3. Direct photon V2 PHENIX, Phys. Rev. Lett. 109, 122302 (2012) • Observed as large as V2 of pions!

4. Too large V2 to explain • Chatterjee et al, arXiv:1305.6443. Puzzle ? !

5. Direct photon V3 Direct photon v3are observed as large as pions, too! pT (GeV/c) PHENIX: S. Mizuno QM2014

6. More puzzling What’s hot, what’s not ? Talk by Rene Bellwied At 3rd International Symposium on Non-equilibrium Dynamics Crete Greece, June 2014.

7. Direct Photon Sources FML, K.Werner, J.Phys.G, 36(2009)035101. • Leading Order (LO) contribution Jets lose energy will effect! 2. Fragmentation contribution (Frag.) Jet + Plasma  reduce photons Thermal contribution from QGP and HG 4. Jet-photon conversion (JPC) Jet + Plasma  enhance photons

8. D :E-loss per unit distance in BDMPS formulism Constrain jet energy loss : QGP fraction A common D=1.5 for various Centralities! FML, T.Hirano, K.Werner, Y. Zhu, Phys.Rev.C79,014905(2009)

9. Competition of sources FML, T.Hirano, K.Werner, Y. Zhu, J.Phys.G, 36 (2009) 064072. Phys.Rev.C79 (2009) 014905. Pt spectra are well understood with hadron date constrained hydro! Energy loss reduces frag., but JPC makes up. High pt photon data show almost a cancelation!

10. P P Simplify Direct Photon Sources Based on High pt direct photon data • 1.Prompt photons • 2. Thermal photons Dominant at high pt , zero v2. Dominate at low pt, u, T  V2(pt) Emission rate : QGP phase-- AMY2001 HG phase -- TRG2004 Question : Photon emission Before QGP formation?

11. Hydro evolution Initial condition: event generator NeXuS, EPOS Evolution: EoSfrom Lattice QCD Freeze-out: + uRQMD for hadron production for photon production EPOS K.Werner, et al, PRC85, 064907 (2012) PRL112, 232301(2014) PRC89.064903 (2014) ….. 3+1 D hydro, viscosityeffects:Q.Shen’s talk

12. Bulk Hadrons & Thermal Photons Hydro initial time • Hadrons are not sensitive to it! • Photons are extremely sensitive to it! Questions: • How big should be ? • How is the system before ?

13. From nPDF toward QGP • Thermalization • Chemical equilibrium – balance btw quarks and gluons from a gluon-dominant system to a QGP Glasma, L.Mclerran by AleksiKurkela, QM2014

14. My Treatment to Glasma • Thermal equilibrium • Chemical equilibrium Quark distribution quark fugacity , better to get from transport theory. Modeling ξ: increase from almost zero at saturate to unity at at midrapidity.

15. Photon emission rate in non-eq. Transport theory: Note: EoS arXiv: 1305.5284 A matter at highT but low photon emission rate! Photon emission rate will be suppressed by a factor of for diagrams with n-quark incoming lines:

16. Is hydro evolution still valid, concerning to hadron data constraints? Yes, because QGP is formed before hadrons freeze-out: particle yields, v2/n scaling.. Before QGP formation, dynamical EoS e=e(P) remains approximately the same, no matter the value of quark fugacity.

17. The Whole Photon Emission • QGP phase-- AMY2001 • HG phase -- TRG2004

18. Spectrum, v2, v3, v4 ... • In E-b-E case, vary with event, pt and PID. However, it is easy to show • So we can get • Then take event average. One for all, based on : average over all particles in each event

19. Two more reasons to distinguish • Small limit • Lesson from pp at 7TeV

20. Q: If is extremely small, what will happen? A: Very hot system! Then… 300MeV 500MeV 700MeV 900MeV

21. Photon Spectrum Small τQGP Large High tail from thermal photons, harder than prompt photons, if we don’t distinguish

22. A lesson from ppat 7TeV Motivated by Ridge in pp, hydro evolution was constructed. ALICE Data tells us: It’s necessary to distinguish Otherwise, overestimate photons! FML, K.Werner, Phys.Rev.Lett.106:242301,(2011)

23. Results: (0.35fm/c) . Extract with 1. Pb+Pb 2.76TeV EPOS217v3 2. Au+Au 200GeV EPOS3102 ξ(τ,…). FML and Sheng-Xu Liu, Phys.Rev.C 89, 034906 (2014)

24. Pb+Pb 2.76TeV EPOS217v3 Thermal photons with different Hadron FO constrains the spectrum of very low pt region. modifies the slope and v2 of thermal photons!

25. Prompt + Thermal photons QGP formation time has strong effects on v2. So does v3, v4, ….

26. Extract QGP formation time are extracted from data.

27. Predict high order harmonics High order harmonics of direct photons are comparable of pions.

28. Au+Au at 200GeV 0-20% EPOS 3.102 Right Preliminary Left

29. Au+Au 200GeV 20-40% A little too hot! Preliminary V3-c% dependence

30. Predict high order harmonics Preliminary

31. Au+Au at 200GeV 0-20% Preliminary Made by Sheng-Xu Liu

32. Conclusions • Glasmais the key to solve photon puzzles. • Photon data carry us unique information of the early stage ! • Early stage of HIC provides us a special example, massive but “dark”, useful for astrophysics and cosmology. Thank you for your attention!