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Study the early stage of heavy ion collisions with direct photons

Study the early stage of heavy ion collisions with direct photons. Fu-Ming Liu （刘复明） Central China Normal University （ 华中师范大学）. HNP2013. 201 3 . 7 .1 8 -12 Zhangjiajie. Outline. Introduction: heavy i on c ollisions and QGP formation Puzzle:

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Study the early stage of heavy ion collisions with direct photons

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  1. Study the early stage of heavy ion collisions with direct photons Fu-Ming Liu （刘复明） Central China Normal University （华中师范大学） HNP2013 2013.7.18-12 Zhangjiajie

  2. Outline • Introduction: heavy ion collisions and QGP formation • Puzzle: the observed large elliptic flow of EM probes • Efforts to solve the large elliptic flow puzzle • Conclusions and Discussions 2

  3. Heavy Ion Collisions and QGP signals

  4. Heavy Ion Collisionsand QGP • Questions: When is QGP formed? How is QGP formed? (unperturbative) The early stage of HIC is indeed poorly known. HIC ==> QGP  HG  dilute hadrons γ dileptons Detectors EM : emitted during the “whole” evolution, called as “golden probes” of QGP, sensitive to the early stage. 4

  5. Photons and dileptons from Plasma PHENIX, Phys. Rev. Lett. 104, 132301 (2010) STAR, arXiv: 1305.5447

  6. Puzzles: Large v2 of EM probes PHENIX, Phys. Rev. Lett. 109, 122302 (2012), large v2 of direct photons v2~15% STAR, arXiv: 1305.5447, Large v2 of dileptons, As large as hadronic v2!

  7. Large v2 of direct photons at LHC! Quark Matter 2012 ArXiv: 1212.3995 7

  8. Why Large v2 of EM probes is a puzzle? Why as large as hadronic v2 is even more puzzle?

  9. Elliptic flow and triangle flow…

  10. Large v2, why puzzle Averaged initial condition Asymmetry Flow, Lorentz boost  v2 Hadrons are produced later, where flow velocity is big. Thermal photons are mostly produced earlier/inner, where flow is weak. 10

  11. Expected Ellptic flow of photons FML, T.Hirano, K.Werner, Y. Zhu, Phys.Rev.C80:034905,2009. Chatterjee et al, arXiv:1305.6443 . Observed v2 is much large than expected, by a large factor, ~ 5 ! It is difficult to explain a factor of 5 with viscosity, fluctuation,… .

  12. Suggestion 1: new photon sources • Conformal anomaly as a photon source (Basar, Kharzeev, Skokov, PRL2012) Problem: Not vanish at large pt. PHENIX, Phys. Rev. Lett. 109, 152302 (2012) 12

  13. Suggestion 2: Shuryakscenerio Shuryak, PRL (1993). Start from glue system due to PDF Prompt γ like in pp, zero v2 Quark fugacity A suppression of early emission looks helpful, but High T due to small ξ !  High emission rate at early stage. Very little help to the puzzle !

  14. Suggest a Shurak-like scenario Prompt γ like in pp, zero v2; Quark fugacity No modification of T with ξ ! Hadronic data (rapidity distribution, pt spectra and v2, …) constrain the entropy density, freeze-out T, later flow.. Take photon data to determine

  15. AuAu direct photons at RHIC Surprise: Pt spectra are not sensitive to . Large v2 implies .

  16. Pb+PbDirect photons at LHC Large v2 implies , too. Predictions:

  17. Conclusion: Shurak-like scenario Prompt γ like in pp at τ =0. Quark fugacity Bad side: Suppress early emission with ξ, but no modification of T ! Emission at glue stage via gg->qq-> g γ loop diagram? The system before is still poorly known. Good side: A natural solution for large v2 of dileptons, Glue can not couple to photons (real and virtual) directly, providing us a “dark matter” during (0, ).

  18. Thank you!

  19. Constrain system evolution (LHC) K.Werner, et al, PRC85, 064907 (2012) Hydro equation: Parameters fixed with hadron data Tau0=0.35 fm/c. Hadron data is more sensitive to freeze-out than to initialization.

  20. Constrain system evolution (RHIC) T.Hirano, et al, PRC77, 044909(2008)

  21. Pb+Pbthermal photons Begin to count thermal photons from 3-flavour QGP at tau=0.35, 0.75, …(fm/c)

  22. thermal photon v2 Flow generates with time, so does v2.

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