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Intermediate-mass lepton pairs in relativistic heavy-ion collisions

Intermediate-mass lepton pairs in relativistic heavy-ion collisions. Charles Gale McGill. Introduction and Outline. New physics: collective, many-body effects Quark-gluon plasma In-medium modifications Modified spectral densities Chiral symmetry restoration Mixing effects

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Intermediate-mass lepton pairs in relativistic heavy-ion collisions

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  1. Intermediate-mass lepton pairsin relativistic heavy-ion collisions Charles Gale McGill

  2. Introduction and Outline • New physics: collective, many-body effects • Quark-gluon plasma • In-medium modifications • Modified spectral densities • Chiral symmetry restoration • Mixing effects • Pion dispersion relation • The physics of (very) hot and dense matter is best explored in the laboratory with relativistic nuclear collisions • Photons and dileptons are penetrating probes

  3. Outline, cont’nd • Experiments (IM): DLS, Helios, NA-38, -50, -60 CERES,WA98, HADES, PHENIX • Electromagnetic radiation as a tool for hadronic tomography: • Low mass dileptons • Intermediate mass dileptons • Low pT photons • High pT photons • High pT intermediate mass dileptons SPS Sangyong Jeon’s talk RHIC LHC

  4. Why? Investigation of the QCD phase diagram F. Karsch, E. Laermann, hep-lat/0305025 S. B. Ruster et al., PRD 72, 034004 (2005)

  5. How? 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

  6. 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

  7. 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

  8. Vector Meson Spectral Densities: A Sample Calculation I Ralf Rapp and Charles Gale, Phys. Rev. C 60, 024003 (1999)

  9. The interaction is constrained by basic hadronic phenomenology Chiral, Massive Yang-Mills: O. Kaymakcalan, S. Rajeev, J. Schechter, PRD 30, 594 (1984) • Parameters and form factors are constrained by • hadronic phenomenology: • Masses & strong decay widths • Electromagnetic decay widths • Other hadronic observables: • e.g.

  10. Low Masses:Vector Meson Spectral Densities:Hot Meson Gas The spectral density is flattened and broadened. Even more with baryons. Rapp, Gale (PRC, 99)

  11. NA60 Comparison of data to RW, BR and Vacuum  New! Sanja Damjanovic Quark Matter 05 (and this meeting) pT dependence

  12. Two approaches: H. Van Hess, R. Rapp, nucl-th/0603084 T. Renk, J. Ruppert, hep-ph/0603110 See J. Ruppert’s talk this aft. Many-body (in-medium) effects are observed!

  13. 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. Shor, PLB 233, 231 (1989)

  14. On the dangers of extrapolations… • (a) B. A. Li, Phys. Rev D 52, 5165 (1995). • (b) Gomm, Kaymakcalan, Schechter, Phys. Rev. D 30, 2345 (1984). • (c) Janssen, Holinde, Speth, Phys. Rev. C 49, 2763 (1994). • (d) Ko, Rudaz, Phys. Rev. D 50, 6867 (1994). • (e) Xiong, Shuryak, Brown, Phys. Rev. D 46, 3798 (1992). Gao & Gale, PRC 57, 254 (1998) But, a lot of data exists!...

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

  16. I. Kvasnikova, C. Gale, and D. K. Srivastava, PRC 65, 064903 (2002) Z. Huang, PL B361, 131 (1995)

  17. A larger comparison • Agreement across theoretical models • Those channels are mostly 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 (A. David’s talk) 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. Intermediate-mass excess is not charm enhancement! • The new 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. A recent analysis: (van Hees & Rapp, hep-ph/0603084) • Sensitive to the space-time modeling: • Still sensitive to the low-mass spectral densities Analyses should be redone with those

  23. Homework • Unite (standardize?) space-time modeling [nD hydro, fireballs, transport approaches…]. • The power of the data is fully realized if a general-purpose acceptance filter exists. (On the way!...) • Chiral symmetry? Still not obvious… An independent access to a1 spectral density is missing. More work on the theory side too. (Urban, Buballa, Hochsch. & Wambach, PRL, 88, 042002 (2002))

  24. leading particle hadrons q q hadrons leading particle leading particle suppressed hadrons q q hadrons leading particle suppressed Jet-quenching Source of energy loss: medium-induced gluon Bremsstrahlung (+ elastic scattering?)

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

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

  27. Dilepton sources • Drell-Yan dileptons • Thermal dileptons • Jet-virtual photon conversion

  28. 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

  29. E loss/gain: some systematics • Includes E gain • Evolves the whole • distribution function S. Jeon’s talk

  30. Jet characteristics:

  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. Jet-plasma dileptons? • Same basic idea as photons, details are slightly different: • High pT cut helps with background subtraction • Go beyond LO, do a HTL analysis

  33. The thermal “baseline” calculation agrees with that of M. Thoma, C. T. Traxler, Phys. Rev. D 56, 198 (1997)

  34. Dileptons from jet-thermal interactions • Jet-thermal as large as DY/heavy quark decay (RHIC) • Jet-thermal still as large as DY. S/B could improve with harder pT cut. • At RHIC, there is a contribution to the IM region • In-medium jet bremsstrahlung will also add to the signal • No heavy quark energy loss • Signal as large as it is for photons Turbide, Gale, Srivastava, Fries, PRC (2006)

  35. But: other signature of jet-photon conversion? • Jet-plasma photons will come out of the hadron-blind region. “Optical” v2 < 0 Turbide, Gale, Fries (PRL 06)

  36. Photons from primordial interactions and fragmenting jets All photons (NN, frag, jet-photon conv., bremss., Th.) 0 + - - +

  37. v2 from “Isolated photon cut” is negative • Photons associated with a “crowded photon cut” show v2 with changing sign • Same game can be played with dileptons (in progress) • See talk by U. Heinz Similar story for the LHC

  38. Jet-plasma interactions: measurable EM signatures! These are fairly robust with respect to changing temperature & dynamics Conclusions, part I • Intermediate-mass dileptons • New data will put further stringent tests on models, both rates & space-time modeling • RHIC & LHC: • Jet-plasma interactions: dilepton channel: signal competes with Drell-Yan (NLO) Towards a consistent treatment of jets & EM radiation

  39. Conclusions, part II • Low and mass dileptons: NA60 data can distinguish between models. In-medium effects! • RHIC/LHC: 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 • EM radiation and hard probes: the start of a beautiful friendship… • EM radiation: change of paradigm

  40. Interested in the techniques discussed here? • Want to know more? Found where fine books are sold (July 2006)

  41. Chatterjee, Frodermann, Heinz, Srivastava, nucl-th/0511079

  42. Jet-plasma photons: • S. Jeon’s talk

  43. New (preliminary) PHENIX Data

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

  45. Soft photons @ RHIC: • There is a window Turbide, Rapp & Gale PRC (2004)

  46. Same spectral densities:Low mass dileptons and real photons S. Turbide, R. Rapp, and C. Gale, PRC (2004)

  47. 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

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