1. Charles Gale McGill (Towards) A consistent tomography of matter under extreme conditions with electromagnetic radiation Hard probes, (some) hard facts; perfect fluids, and sticky issues…

2. Charles Gale McGill Outline Information revealed by photon measurements Dynamics of heavy ion collisions: link between the soft and hard sectors Details of photon measurement @ RHIC Photon azimuthal anisotropy Photon tagged-jets: a clean probe of jet energy loss? Conclusions

3. Charles Gale McGill What is tomography and what is it good for? Medical diagnostics tool: Medical Imaging Recreation of an object (2D-3D) from a series of X-ray images –Properties of the source are known and calibrated –Probes propagate through the medium. Interaction is known, medium is known and stable –Image(s) reconstructed

4. Charles Gale McGill The “patient” here is hot and dense strongly interacting matter. Trying to get info about the QCD phase diagram S. B. Ruster et al., PRD 72, 034004 (2005) F. Karsch, E. Laermann, hep-lat/0305025

5. Charles Gale McGill 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 Need a model for the dynamics of the HI collision McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91)

6. Charles Gale McGill Caution: not all dynamical models are the same… Microscopic transport models (UrQMD, HSD…) Hydrodynamic models Thermal fireball models Those differ in details (symmetry assumptions, chemical potentials, freezeout conditions, cross sections…) Need to be constrained by hadronic observables!

7. Charles Gale McGill Sources: 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

8. Charles Gale McGill Going to two loops: Aurenche, Kobes, Gelis, Petitgirard (1996) Aurenche, Gelis, Kobes, Zaraket (1998) Co-linear singularities: AMY, Arnold, Moore, and Yaffe, JHEP 12, 009 (2001); JHEP 11, 057 (2001): incorporates LPM; photon rates complete to leading order in α s Can be expressed in terms of the solution to a linear integral equation

9. Charles Gale McGill Electromagnetic radiation (photons) from hadrons at the SPS used to make predictions for RHIC Details in Turbide, Rapp, Gale, PRC (2004) Same spectral densities as used for dileptons Low momentum radiation from thermal sources Hadronic sources: WA98 & NA60

10. Charles Gale McGill Photons: Same spectral densities as low mass dileptons Same dynamical model; same boundary conditions Cronin contribution estimated from pA data (E629, NA3) QGP: small Turbide, Rapp & Gale PRC 2004 Ruppert et al. PRL 2008

11. Charles Gale McGill RHIC: jet-quenching Azimuthal correlation: –Shows the absence of “away-side” jet. Pedestal&flow subtracted

12. Charles Gale McGill hadrons q q leading particle leading particle Jet-quenching = tomography hadrons q q leading particle suppressed leading particle suppressed Dominant source of energy loss: medium-induced gluon bremsstrahlung? However, see later…

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

14. Charles Gale McGill Sources of photons: Hard direct photons. pQCD with shadowing Non-thermal Fragmentation photons. pQCD with shadowing Non-thermal Thermal photons Thermal Jet in-medium bremsstrahlung Thermal Jet-plasma photons Thermal

15. Charles Gale McGill A theoretical connection between jet energy loss and the electromagnetic emissivity Use again 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

16. Charles Gale McGill E loss/gain: some systematics Includes E gain Evolves the whole distribution function

17. Charles Gale McGill Time-evolution of a parton distribution The entire distribution is evolved by the collision Kernel(s) of the FP equation Turbide, Gale, Jeon, and Moore (2004)

18. Charles Gale McGill PHENIX hadronic data B. Cole, QM 05

19. Charles Gale McGill Photons: establishing a baseline QCD @ NLO, Aurenche et al., NPB 286, 553 (1987) See also Gordon & Vogelsang Turbide, Gale, Frodermann, Heinz, PRC (2008). Photons from AA in a couple of slides…

20. Charles Gale McGill But: other signature of jet-photon conversion? Jet-plasma photons will come out of the hadron-blind region. “Optical” v2 < 0 Suggestion & high p T : Turbide, Gale, Fries PRL (2006) Low p T : Chatterjee et al., PRL (2006) All p T : Turbide et al., PRC (2008)

21. Charles Gale McGill Data: Results from PHENIX v2: small! Consistent with zero (within errors) T. Sakaguchi RHIC/AGS 07

22. Charles Gale McGill AZHYDRO (Heinz & Kolb) (c.f. Quark Gluon Plasma III) T c =164 MeV, =0.2 fm/c, T fo =130 MeV Good modeling of bulk dynamics Small values of momentum anisotropies Geometric anisotropy shrinks rapidly

23. Charles Gale McGill Results: Spectra Window for thermal effects at low to intermediate p T Same dynamical model as hadronic data NO additional parameters in the EM fits, over the hadronic fits The preliminary experimental data is being finalized

24. Charles Gale McGill Results: R AA The discrimination between models is dependent on the high p T photons See also F. Arleo, JHEP (2007)

25. Charles Gale McGill Results: v 2

26. Charles Gale McGill Results: v 2 sensitivity Good news: high p T photon v2 sensitive to details of initial conditions (geometric isotropy) Some additional resolution with correlation analyses: Jet bremsstrahlung/fragmentation correlated with hadrons Jet-plasma & thermal, uncorrelated

27. Charles Gale McGill Dileptons? Dusling & Zahed, arXiv:0712.1982 E. L. Bratkovskaya, W. Cassing, O. Lynnyk, arXiv:0805.3177 H. Van Hees, QM08

28. Charles Gale McGill Energy loss systematics with collisional energy loss (along with radiative). What next? New development G. Qin, J. Ruppert, C. Gale, S. Jeon, G. D. Moore, M. G. Mustafa, PRL (2008) There is (some) room to re- examine the effect on EM emission

29. Charles Gale McGill Photon-tagged jets X.-N. Wang, Huang, Sarcevic., Phys. Rev. Lett. 77, 231 - 234 (1996) At LO the photon is strongly correlated with the away-side jet LO Proposed advantage: Calibrated probe of the QGP. At LO: In h-jet azimuthal correlations E leading particle  E parent parton In  -jet azimuthal correlations E  =E parent parton How does it look in a full calculation?

30. Charles Gale McGill But, recall sources of photons: Hard direct photons. pQCD with shadowing Non-thermal Fragmentation photons. pQCD with shadowing Non-thermal Thermal photons Thermal Jet in-medium bremmstrahlung Thermal Jet-plasma photons Thermal

31. Charles Gale McGill Some definitions… The hadron spectrum, given a trigger photon Joint probability for producing a back-to-back pair Initial distribution of away-side jet before evolution in the medium Yield per trigger in AA collisions/yield per trigger in pp collision Inclusive fragmentation function in AA/ (…) in pp

32. Charles Gale McGill 3D Hydro results address all data in the soft sector with one consistent approach b=6.3 fm Nonaka & Bass: PRC75, 014902 (2007)

33. Charles Gale McGill The initial momentum distribution of the away-side jet (direct component not shown) in central Au – Au @ RHIC Different contributions to yield per trigger for photon-tagged  0 in central Au – Au @ RHIC Results (with coll. E loss) Qin et al., in preparation

34. Charles Gale McGill Conclusions Photons and hard probes (e.g. jets) can and should be treated together and consistently The RHIC data is totally compatible with a picture where jets loose energy (radiative + elastic), and where plasma channels participate in both energy loss and photon production Photon and hard probes help in the modeling of soft matter Viscosity? Do dileptons (in progress) LHC (in progress) The future is bright!