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Thermal radiation from QGP and Lattice QCD P é ter Petreczky Nuclear Theory Group and RIKEN-BNL

Thermal radiation from QGP and Lattice QCD P é ter Petreczky Nuclear Theory Group and RIKEN-BNL Physics Department Brookhaven National Laboratory. Production rate of thermal photons and dileptos. spectral functions. Lattice QCD calculations.

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Thermal radiation from QGP and Lattice QCD P é ter Petreczky Nuclear Theory Group and RIKEN-BNL

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  1. Thermal radiation from QGP and Lattice QCD Péter Petreczky Nuclear Theory Group and RIKEN-BNL Physics Department Brookhaven National Laboratory Production rate of thermal photons and dileptos spectral functions Lattice QCD calculations Current-current correlator in Eucledian time Motivations : coupling constant is large close to but even at very high temperatures non-perturbative effects are important at the momentum scale RHIC II Workshop, BNL, April 29-30, 2005

  2. Meson correlators and spectral functions Thermal dilepton rate: Thermal photon rate: McLerran, Toimela, PRD 31 (85) 545 LQCD MEM

  3. Lattice setup Quenched QCD with Wilson fermions Isotropic Lattice Anisotropic Lattice time space space Karsch, Laermann, Petreczky, Stickan, Wetzorke, PLB 530 (02) 147 Non-perturbatively impr. Wilson action Asakasa, Hatsuda, Nakahara, NPA 715 (03) 863 Std. Wilson action

  4. Reconstruction of the spectral functions data and degrees of freedom to reconstruct Bayesian techniques: find which maximizes data Prior knowledge Maximum Entropy Method (MEM) Asakawa, Hatsuda, Nakahara, PRD 60 (99) 091503, Prog. Part. Nucl. Phys. 46 (01) 459 Likelihood function Shannon-Janes entropy: -perturbation theory - default model

  5. Numerical results on the correlator of the vector currents Lattice spacing dependence is small ! constraints on the spectral functions at small energies

  6. Vector spectral functions above deconfinement Karsch, Laermann, Petreczky, Stickan, Wetzorke, PLB 530 (02) 147 Asakasa, Hatsuda, Nakahara, NPA 715 (03) 863 ?? lattice artifacts Mesons below

  7. Spectral function and thermal dilepton rate Karsch, Laermann, Petreczky, Stickan, Wetzorke, PLB 530 (02) 147 suppression of low mass dileptons in sharp contradiction with perturbative expectations predicting enhancement at low energy Braaten, Pisarski, Yuan, PRL 64 (90) 2242

  8. Spectral functions at finite momenta

  9. Removing lattice artifacts in the spectral functions Free spectral functions Wilson fermions Highly improved (HYP) fermions

  10. Removing lattice artifacts in the spectral functions Free spectral functions Wilson fermions Highly improved (HYP) fermions Karsch, Laermann, Petreczky, Stickan, Phys. Rev. D68 (03) 014504

  11. Summary • Lattice calculations of the vector current correlators together • with MEM can provide some informations about thermal radiation • Current calculations suggest suppression of low mass thermal • dileptons compared to the naïve perturbative predictions and • possibly very small photon rate • Lattice artifacts in these calculations are a problem; they are • under control at the level of the correlation functions but need • to be understood in the spectal functions => highly improved actions

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