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Thermal Radiation Workshop (2012)

Motivation & Plans

Dileptons and photons are a crucial probe of the strongly interacting matter created in ultra-relativistic heavy ion collisions. Leptons and photons are produced during the whole evolution of the created matter and can traverse the medium with minimal interactions. Different kinematics of lepton pairs and photons can selectively probe the properties of the formed matter throughout its entire evolution. Electromagnetic radiation thus constitutes a class of penetrating probes, complementary to hadronic observables. Of particular interest to us is the promise that thermal radiation from the early phases of the formed matter can be extracted from experimental data by subtracting known contributions from hadron decays after freeze out and primordial production via hard processes.

Thermal radiation may result from the hadronic or partonic phase. Radiation from the hadronic phase would mostly result from pp annihilation and thus is not only sensitive to the thermal properties but also to medium modification of the short lived vector mesons and thus to effects of the chiral transition. At higher masses, say above 1 GeV thermal radiation from the partonic phase is expected to dominate. Through a careful analysis of the mass and momentum dependence of the thermal radiation, information about the early thermal properties and the space-time evolution of the formed matter may be extracted.

Recently, many new dilepton and direct photon results have been reported covering a broad beam energy range from RHIC to LHC, together with the published SPS measurements. More specifically, the substantial v2 observed by PHENIX for direct photons at 1 < pT < 4 GeV/c in Au+Au collisions at 200 GeV, the large dielectron enhancement measured by PHENIX in the low mass and low pT region in 200 GeV central Au+Au collisions, new dielectron results from Hadron Blind Detector (HBD) analysis in 200 GeV Au+Au collisions from PHENIX, and dielectron measurements in Au+Au collisions from 19.6 to 200 GeV by STAR, have challenged our understanding and have motivated a lot of new theoretical calculations. RHIC results are now the driving force behind the advances in the electromagnetic sector.

We would like to bring together theorists and experimentalists for an in-depth discussion of these results. It is very important for the heavy ion program to reach a systematic understanding across different beam energies. We also would like to discuss how future detector upgrades at RHIC will advance our understanding.

Topics to be discussed will include:

  • Physics of modified spectral functions from dilepton measurements from SPS to LHC energies.
  • Physics behind thermal photon emission.
  • Experimental results on dileptons and thermal photons.
  • Future measurements on dileptons and thermal photons.


Presentations will be mainly by invitation. We expect to be able to accommodate a limited number of contributed talks. If you are interested in presenting a contributed talk, please contact Lijuan Ruan at

Workshop Organizers

  • Yasuyuki Akiba (RIKEN Nishina Center/RBRC)
  • Axel Drees (Stony Brook University)
  • Rainer Fries (Texas A&M)
  • Charles Gale (McGill University)
  • Lijuan Ruan (BNL)

Special Evening Event

Registered attendees are invited to attend the optional banquet dinner after the Workshop on Thursday, December 6, 2012 at the Brookhaven Center South Room; free of charge for registered participants. Directions

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Last Modified: October 17, 2012