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Thermal Photons and Dileptons*

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…). Why? The information carried by EM probes. Emission rates:. [photons].

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Thermal Photons and Dileptons*

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  1. Thermal Photons and Dileptons* • Why? How? Theory • Low mass dileptons • Intermediate mass dileptons • Photons: low and high(er) pT photons • EM signature of jets (* Not an exhaustive review…)

  2. Why? The information carried by EM probes Emission rates: [photons] McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91) [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

  3. 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. 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. Expectations, part II • Thermal QGP plasma radiation • Many-body, in-medium, effects on spectral densities Weinberg (67) Kapusta, Shuryak (94) + other possibilities…

  6. UrQMD In-medium: what medium? Phase-space trajectory goes through qualitatively different media

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

  8. Vector Meson Spectral Densities, II(adding baryons) R. Rapp & J.Wambach, 1999

  9. Vector spectral densities from data 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) • Should hold near the mass-shell • Adler decoupling enforced

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

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

  12. e+e- mass spectrum: comparison to the models Sergey Yurevich (CERES) 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

  13. NA60 Comparison of data to RW, BR and Vacuum  Sanja Damjanovic pT dependence

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

  15. NA50Pb-Pb 158 GeV DY charm central collisions _ DY DD 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! A. Shor, PLB 233, 231 (1989)

  16. e+ e- Data: A Wealth of Information • OLYA • CMD • DM-1(2) • ARGUS • M3N • gg2

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

  19. 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. 1 NA60 IMR analysis: weighted offset fits (R. Shahoyan) Extract prompts by fixing Open Charm contribution Fix Charm contribution to “world average” value or Fix Charm contribution to NA50 p-A expected value  Fit always requires ~2 times more Prompts

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

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

  27. Pedestal&flow subtracted Azimuthal correlation • Shows the absence of “away-side” jet.

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

  29. Photon sources • Hard direct photons • EM bremsstrahlung • Thermal photons from hot medium • Jet-photon conversion • Jet in-medium bremsstrahlung

  30. 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

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

  32. With the new (preliminary) PHENIX data

  33. Photons: establishing a baseline (preliminary) Aurenche et al., NPB 286, 553 (1987) Consistent with Gordon & Vogelsang

  34. p+p and d+Au spectra compared to NLO pQCD Direct g in d+Au (S. Bathe) • ratio to NLO pQCD • consistent with 1 • No indication for nuclear effects 2 Poster H. Torii Poster D. Peressounko

  35. RHIC jet-plasma photons With E loss

  36. RHIC Au Au data

  37. 0-30 90-140 200-300 140-200 MeV Rdata ÷ ÷ ÷ New (preliminary) PHENIX Data(Bathe, Buesching)

  38. New (preliminary) PHENIX Data(Bathe, Buesching) A prediction: all source Sizes fixed prior to QM

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

  40. If photons can be detected in coincidence with hadrons The jet-plasma photons can be easier to isolate (Cole)

  41. Jet-plasma interactions: measurable EM signatures! • RHIC: • Jet-plasma interaction is a large source of photons up to pT ~ 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

  42. 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…

  43. Collaborators: Simon Turbide, McGill University Rainer Fries, University of Minnesota R. Rapp, Texas A&M Dinesh Srivastava, VECC, Calcutta

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