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Electromagnetic radiation from nuclear collisions @ RHIC energies

Electromagnetic radiation from nuclear collisions @ RHIC energies. Outline: Electromagnetic production processes & what they reveal Hadronic and partonic sectors Characteristics of sources Comparison with RHIC data (photons) Conclusions. The information carried by EM radiation. f. k. i.

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Electromagnetic radiation from nuclear collisions @ RHIC energies

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  1. Electromagnetic radiation from nuclear collisions @ RHIC energies • Outline: • Electromagnetic production processes & what they reveal • Hadronic and partonic sectors • Characteristics of sources • Comparison with RHIC data (photons) • Conclusions

  2. The information carried by EM radiation f k i [photons] [dileptons] [photons] absorption emission

  3. 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 • Need a model for the dynamics of the HI collision

  4. 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!

  5. 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

  6. 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 αs Can be expressed in terms of the solution to a linear integral equation

  7. Electromagnetic radiation (photons) from hadrons • Details in Turbide, Rapp, Gale, PRC (2004) • Same spectral densities as used for dileptons • Low momentum radiation from thermal sources

  8. Pedestal&flow subtracted RHIC: jet-quenching Azimuthal correlation: • Shows the absence of “away-side” jet.

  9. leading particle hadrons q q hadrons leading particle leading particle suppressed hadrons q q hadrons leading particle suppressed Jet-quenching Dominant source of energy loss: medium-induced gluon bremsstrahlung? However, see later…

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

  11. Sources of photons: Hard direct photons. pQCD with shadowing Non-thermal Fragmentation photons. pQCD with shadowing Non-thermal Radiations thermal photons Thermal Jet-plasma photons Thermal Jet in-medium bremmstrahlung Thermal

  12. 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

  13. E loss/gain: some systematics • Includes E gain • Evolves the whole • distribution function

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

  15. PHENIX data B. Cole, QM 05

  16. Photons: establishing a baseline Turbide, Gale, Frodermann, Heinz, PRC (2008) in press. QCD @ NLO, Aurenche et al., NPB 286, 553 (1987) See also Gordon & Vogelsang

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

  18. Simple dynamics: Turbide, Gale, Fries PRL (2006) Photons from primordial interactions and fragmenting jets All photons (NN, frag, jet-photon conv., bremss., Th.) 0 + - - +

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

  20. AZHYDRO (Heinz & Kolb)(c.f. Quark Gluon Plasma III) • Tc=164 MeV, =0.2 fm/c, Tfo=130 MeV • Good modeling of bulk dynamics • Small values of momentum anisotropies • Geometric anisotropy shrinks rapidly

  21. Results: Spectra • Window for thermal effects at low to intermediate pT • Same dynamical model as hadronic data • NO sdditional parameters in the EM fits, over the hadronic fits • The preliminary experimental data is being finalized

  22. Results: RAA The discrimination between models is dependent on the high pT photons See also F. Arleo, JHEP (2007)

  23. Results: v2

  24. Results: v2 sensitivity Some additional resolution with correlation analyses: • Jet bremsstrahlung/fragmentation correlated with hadrons • Jet-plasma & thermal, uncorrelated Good news: high pT photon v2 sensitive to details of initial conditions (geometric isotropy)

  25. Results: dileptons • A thermal component is expected over the purely thermal radiation • Caveat: correlated charm not shown • LHC dileptons: in progress

  26. What next? G. Qin, J. Ruppert, C. Gale, S. Jeon, G. D. Moore, M. G. Mustafa, PRL (2008) in press. arXiv:0710.0605 New: Energy loss systematics in AMY with collisional energy loss (along with radiative). See Guang-You Qin’s poster There is (some) room to re-examine the effect on EM emission

  27. Electromagnetic signals @ RHIC: great results • Important progress towards an inclusive treatment of EM radiation and hadronic observables (more work to do) • Important progress towards an inclusive treatment of jet energy loss and EM emissivities (more work to do) • Spectra and elliptic flow: compatible with data • v2: a sensitive probe • Hope of making more progress with (anti-)isolation cuts • LHC: • Jet-plasma photon signal is also important

  28. RHIC photons: estimates with a thermal model • With E loss • LHC also done Turbide, Gale, Jeon, and Moore PRC (2004)

  29. 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

  30. LHC photons estimates Turbide, Gale, Jeon, and Moore PRC (2004) See also T. Sakaguchi, this conference

  31. How big (small) is this? Turbide, Rapp & Gale PRC (2004) Phenomenological Exploration…

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