Direct Photons and Photon-Hadron Correlations at PHENIX
  Direct photons are a powerful tool to study the hot and dense matter created in heavy-ion collisions at RHIC, since they are created in the different stages of the collision. Since they do not interact via the strong force, they can travel through the hot and dense matter mostly unaffected. The PHENIX experiment has measured direct photons using different methods, over a broad range of transverse momentum (\pt), in different collision systems, and at different energies. These measurements help interpreting the measurement of hadrons as well as understanding the temperature of the created quark-gluon plasma (QGP). The azimuthal anisotropy of direct photons may shed light on the thermalization time of the medium. Using direct photons to tag jets is a crucial tool to understand the energy loss of scattered partons in the medium. 
Baldo Sahlmueller (for the PHENIX Collaboration)
nucl-ex