We study the thermal emission of photons from hot and dense strongly interacting hadronic matter at temperatures close to the expected phase transition to the Quark-Gluon Plasma (QGP). Earlier calculations of photon radiation from ensembles of interacting mesons are re-examined with additional constraints, including new production channels as well as an assessment of hadronic form factor effects. Whereas strangeness-induced photon yields turn out to be moderate, the hitherto not considered t-channel exchange of ω-mesons is found to contribute appreciably for photon energies above ∼ 1.5 GeV. The role of baryonic effects is assessed using existing many-body calculations of lepton pair production. We argue that our combined results constitute a rather realistic emission rate, appropriate for applications in relativistic heavy-ion collisions. Supplemented with recent evaluations of QGP emission, and an estimate for primordial (hard) production, we compute photon spectra at SPS, RHIC and LHC energies.

We calculate the nuclear modification factor of neutral pions and the photon yield at high pT in central Au-Au collisions at RHIC ( √ s =200 GeV) and Pb-Pb collisions at the LHC ( √ s =5500 GeV). A leading-order accurate treatment of jet energy loss in the medium has been convolved with a physical description of the initial spatial distribution of jets and a (1+1) dimensional expansion. We reproduce the nuclear modification factor of pion RAA at RHIC, assuming an initial temperature Ti =370 MeV and a formation time τi =0.26 fm/c, corresponding to dN/dy = 1260. The resulting suppression depends on the particle rapidity density dN/dy but weakly on the initial temperature. The jet energy loss treatment is also included in the calculation of high pT photons. Photons coming from primordial hard N-N scattering are the dominant contribution at RHIC for pT > 5 GeV, while at the LHC, the range 8 < pT < 14 GeV is dominated by jet-photon conversion in the plasma.

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute ‘Heavy Ion Collisions at the LHC—Last Call for Predictions’, held from 14th May to 10th June 2007.

The hot and dense strongly interacting matter created in collisions of heavy nuclei at RHIC energies is modeled with relativistic hydrodynamics, and the spectra of real and virtual photons produced at midrapidity in these events are calculated. Several different sources are considered, and their relative importance is compared. Specifically, we include jet fragmentation, jet-plasma interactions, the emission of radiation from the thermal medium and from primordial hard collisions. Our calculations consistently take into account jet energy loss, as evaluated in the AMY formalism. We obtain results for the spectra, the nuclear modification factor (R γ AA ), and the azimuthal anisotropy (v γ 2 ) that agree with the photon measurements performed by the PHENIX Collaboration at RHIC.