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

2. 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. Our brilliant universe 2

3. Direct photon V 2 PHENIX, Phys. Rev. Lett. 109, 122302 (2012) Observed as large as V 2 of pions! 3

4. Too large V 2 to explain Chatterjee et al, arXiv:1305.6443. Puzzle ? ! 4

5. p T (GeV/c) Direct photon v 3 are observed as large as pions, too! PHENIX: S. Mizuno QM2014 Direct photon V 3 5

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

7. Direct Photon Sources Jets lose energy will effect! 1.Leading Order (LO) contribution 2. Fragmentation contribution (Frag.) 3.Thermal contribution from QGP and HG 4. Jet-photon conversion (JPC) Jet + Plasma  enhance photons Jet + Plasma  reduce photons FML, K.Werner, J.Phys.G, 36(2009)035101. 7

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

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! 9

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

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

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 ? 12

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 Aleksi Kurkela, QM2014 13

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. 14

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

16. Is hydro evolution still valid, concerning to hadron data constraints? Yes, because 1)QGP is formed before hadrons freeze-out : particle yields, v2/n scaling.. 2)Before QGP formation, dynamical EoS e=e(P) remains approximately the same, no matter the value of quark fugacity. 16

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

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 18

19. Two more reasons to distinguish 1.Small limit 2.Lesson from pp at 7TeV 19

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

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

22. A lesson from pp at 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) 22

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) 23

24. Pb+Pb 2.76TeV EPOS217v3 Thermal photons with different 1.Hadron FO constrains the spectrum of very low pt region. 2. modifies the slope and v2 of thermal photons! 24

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

26. Extract QGP formation time are extracted from data. 26

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

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

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

30. Predict high order harmonics Preliminary 30

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

32. Conclusions Glasma is 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! 32