1. Charles Gale McGill QM 2005 Thermal Photons and Dileptons* Why? How? Theory Low mass dileptons Intermediate mass dileptons Photons: low and high(er) p T photons EM signature of jets (* Not an exhaustive review…)

2. Charles Gale McGill QM 2005 Why? The information carried by EM probes Emission rates: [photons] [dileptons] The electromagnetic spectra will be direct probes of the in-medium photon self-energy They are hard probes: EM signals as probes for hadronic tomography McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91)

3. Charles Gale McGill QM 2005 The current-current correlator A model for the hadronic electromagnetic current: VMD The current-field identity (J. J. Sakurai) Spectral density The photon/dilepton signal can tell us about the in-medium spectral densities of vector mesons. Rates need to be integrated over the space-time history, with some dynamical model

4. Charles Gale McGill QM 2005 What is expected (dileptons) Low masses receive significant contribution from radiative decays High masses dominated by DY Intermediate mass region interesting from QGP perspective, (Shuryak (78), Shor (89)) Photons: similar story, but featureless spectra Experiments: DLS, Helios, TAPS, NA38, - 50, WA98, CERES, PHENIX, HADES, NA60

5. Charles Gale McGill QM 2005 Expectations, part II Thermal QGP plasma radiation Many-body, in-medium, effects on spectral densities Weinberg (67) Kapusta, Shuryak (94) + other possibilities…

6. Charles Gale McGill QM 2005 UrQMD In-medium: what medium? Phase-space trajectory goes through qualitatively different media

7. Charles Gale McGill QM 2005 Low Masses:Vector Meson Spectral Densities:Hot Meson Gas The spectral density is flattened and broadened Rapp, Gale (99)

8. Charles Gale McGill QM 2005 Vector Meson Spectral Densities, II (adding baryons) R. Rapp & J.Wambach, 1999

9. Charles Gale McGill QM 2005 Vector spectral densities from data Should hold near the mass-shell Adler decoupling enforced E. V.Shuryak, Nucl. Phys. A 533, 761 (1991); V. L. Eletsky and V. L. Ioffe, Phys. Lett. B 401, 327 (1997); Eletsky, Belkacem, Ellis, Kapusta, Phys. Rev. C 64, 035202 (2001)

10. Charles Gale McGill QM 2005 Two approaches: Rates are also constrained by nuclear photoabsorption data Lagrangians are constrained by hadronic phenomenology Mass shifts & broadening are related by dispersion relations Rapp & Wambach Eletsky, Ioffe, Kapusta (Giessen, Frankfurt, Munich)

11. Charles Gale McGill QM 2005 Fold in With a Dynamical Evolution Model Huovinen, Belkacem, Ellis, and Kapusta (02) What’s new? Rapp, Brown-Rho

12. Charles Gale McGill QM 2005 e+e- mass spectrum: comparison to the models calculation by R.Rapp using Rapp/Wambach medium modification of rho spectral function calculation by R.Rapp using Brown-Rho scaling B. Kämpfer, thermal emission...added to the cocktail. in the 0.8 < m < 0.98 GeV region: Brown-Rho curve:  2 /n = 2.4 the other two curves:  2 /n ~ 0.3 Sergey Yurevich (CERES)

13. Charles Gale McGill QM 2005 NA60 Comparison of data to RW, BR and Vacuum  p T dependence Sanja Damjanovic

14. Charles Gale McGill QM 2005 NA60 Comparison of data to RW, BR and Vacuum  Linear scale!!!Linear scale!!! Quality of data enables a preciseQuality of data enables a precise determination of the spectral determination of the spectral properties. properties. The beginning of a new era…The beginning of a new era…

15. Charles Gale McGill QM 2005 The intermediate mass sector: some background Direct connection to Hard Probes Off-shell effects are potentially important for effective hadronic interactions Gao & Gale, PRC 57, 254 (1998) A lot of data already exists! DD _ DY NA50 Pb-Pb 158 GeV central collisions charm DY A. Shor, PLB 233, 231 (1989)

16. Charles Gale McGill QM 2005 e+ e- Data: A Wealth of Information OLYA CMD DM-1(2) ARGUS M3N 

17. Charles Gale McGill QM 2005 A larger comparison Agreement across theoretical models Those channels are absent from the spectral densities used in comparisons with CERES and the new NA60 data.

18. Charles Gale McGill QM 2005 Li and Gale, PRC (1998) Intermediate mass data A. L. S. Angelis et al. (Helios 3), Eur. Phys. J. (1998) R. Rapp & E. Shuryak, PLB (2000)

19. Charles Gale McGill QM 2005 NA50 Data (cont’nd) I. Kvasnikova, C. Gale, and D. K. Srivastava, PRC 2002 In agreement with multiplicity dependence Includes detector acceptance & efficiency (O. Drapier, NA50)

20. Charles Gale McGill QM 2005 NA60 IMR analysis: weighted offset fits (R. Shahoyan)  or Fix Charm contribution to “world average” value Fix Charm contribution to NA50 p-A expected value Fit always requires ~2 times more Prompts 1 Extract prompts by fixing Open Charm contribution

21. Charles Gale McGill QM 2005 Low and Intermediate masses: partial summary Thermal sources shine in the LMR and IMR. No great sensitivity to the QGP The data is precise enough to consider a differentiation of space-time models DY? At low M, medium-enhanced multiple parton scatterings might be large (Qiu, Zhang (02), Fries, Schaefer, Stein, Mueller (00). pA measurement.)

22. Charles Gale McGill QM 2005 (Theory) Homework Unite (standardize?) space-time modeling [nD hydro, fireballs, transport approaches…]. Rapidity dependence of photon signal: a probe of stopping (Renk, PRC (05)) The power of the data is only fully realized if a general-purpose acceptance filter exists.

23. Charles Gale McGill QM 2005 Electromagnetic radiation from QCD First approaches McLerran, Toimela (1986); Kajantie, Kapusta, McLerran, Mekjian (1986) Baier, Pire, Schiff (1988); Altherr, Ruuskanen (1992) Rates diverge: HTL resummation

24. Charles Gale McGill QM 2005 HTL program: Klimov (1981), Weldon (1982) Braaten & Pisarski (1990); Frenkel & Taylor (1990) Kapusta, Lichard, Seibert (1991) Baier, Nakkagawa, Niegawa, Redlich (1992) Going to two loops: Aurenche, Kobes, Gelis, Petitgirard (1996) Aurenche, Gelis, Kobes, Zaraket (1998) Co-linear singularities:

25. Charles Gale McGill QM 2005 Singularities can be re-summed Arnold, Moore, and Yaffe JHEP 12, 009 (2001); JHEP 11, 057 (2001) Incorporates LPM Complete leading order in α s Inclusive treatment of collinear enhancement, photon and gluon emission Can be expressed in terms of the solution to a linear integral equation

26. Charles Gale McGill QM 2005 How big (small) is this? Turbide, Rapp & Gale PRC (2004)

27. Charles Gale McGill QM 2005

28. Charles Gale McGill QM 2005 Azimuthal correlation –Shows the absence of “away-side” jet. Pedestal&flow subtracted

29. Charles Gale McGill QM 2005 Quenching = Jet-Plasma interaction. Does this have an EM signature? The plasma mediates a jet-photon conversion Fries, Mueller & Srivastava, PRL 90, 132301 (2003)

30. Charles Gale McGill QM 2005 Photon sources Hard direct photons EM bremsstrahlung Thermal photons from hot medium Jet-photon conversion Jet in-medium bremsstrahlung

31. Charles Gale McGill QM 2005 Energy loss in the jet-photon conversion? Jet bremsstrahlung? Use the approach of Arnold, Moore, and Yaffe JHEP 12, 009 (2001); JHEP 11, 057 (2001) Incorporates LPM Complete leading order in  S Inclusive treatment of collinear enhancement, photon and gluon emission Can be expressed in terms of the solution to a linear integral equation

32. Charles Gale McGill QM 2005 Time-evolution of quark distribution The entire distribution is evolved by the collision Kernel(s) Of the FP equation Turbide, Gale, Jeon, and Moore (2004)

33. Charles Gale McGill QM 2005 With the new (preliminary) PHENIX data

34. Charles Gale McGill QM 2005 Photons: establishing a baseline Aurenche et al., NPB 286, 553 (1987) Consistent with Gordon & Vogelsang (preliminary)

35. Charles Gale McGill QM 2005 Direct  in d+Au p+p and d+Au spectra compared to NLO pQCD ratio to NLO pQCD consistent with 1 No indication for nuclear effects 2 Poster H. Torii Poster D. Peressounko (S. Bathe)

36. Charles Gale McGill QM 2005 RHIC jet-plasma photons With E loss

37. Charles Gale McGill QM 2005 RHIC Au Au data

38. Charles Gale McGill QM 2005 New (preliminary) PHENIX Data (Bathe, Buesching) ÷ ÷ ÷ 0-30 90-140 140-200 MeV 200-300 R data

39. Charles Gale McGill QM 2005 New (preliminary) PHENIX Data (Bathe, Buesching) A prediction: all source Sizes fixed prior to QM

40. Charles Gale McGill QM 2005

41. Charles Gale McGill QM 2005 Other signature of jet-photon conversion? Jet-plasma photons will come out of the hadron-blind region. “Optical” v2 < 0 Turbide, Gale, Fries (05)

42. Charles Gale McGill QM 2005 If photons can be detected in coincidence with hadrons The jet-plasma photons can be easier to isolate (Cole)

43. Charles Gale McGill QM 2005 Jet-plasma interactions: measurable EM signatures! RHIC: –Jet-plasma interaction is a large source of photons up to p T ~ 6 GeV. –Conclusions include energy-loss considerations –True also in the dilepton channel: signal competes with Drell-Yan (NLO) LHC: –Jet-plasma photon signal is important –Large mass lepton pairs dominate over Drell-Yan emission. Towards a consistent treatment of jets & EM radiation

44. Charles Gale McGill QM 2005 Summary, Conclusions, Open Issues Low and mass dileptons: NA60 data can distinguish between models IMR: More homework to be done (Higher twist…) Space-time evolution models RHIC: There are measurable electromagnetic signatures of jet-plasma interaction: those constitute complementary observables to signal the existence of conditions suitable for jet-quenching Photon v2, a revealing probe RHIC dileptons: systematic errors still too large to permit source identification (A. Toia, PHENIX) EM radiation and hard probes: the start of a beautiful friendship…

45. Charles Gale McGill QM 2005 Collaborators: Simon Turbide, McGill University Rainer Fries, University of Minnesota R. Rapp, Texas A&M Dinesh Srivastava, VECC, Calcutta