Si Xie(California Institute of Technology (US)), Zoltan Gecse(Fermi National Accelerator Lab. (US))
Photon and Photon+Jet Probes of Heavy Ion Collisions
Events containing a high transverse momentum (pT) prompt photon offer useful tools to study QCD in many hadronic collision systems. In proton+proton collisions, they provide precision tests of perturbative QCD. In proton+nucleus collisions, they are sensitive to a broad set of physics effects such as the modification of the parton densities in nuclei, including the onset of non-linear QCD or saturation effects at low nuclear-x, and the energy loss of partons in the nucleus before the hard scattering. In nucleus+nucleus collisions, they can be used to probe the dynamics of the hot, dense Quark-Gluon Plasma (QGP) medium. Because photons do not carry color charge, they are unaffected by the QGP, and thus provide information about the momentum, direction, and flavor (quark or gluon) of the associated hard-scattered parton before it begins to shower and become quenched. This allows for a detailed exploration of the absolute energy loss and modification of jets by the QGP medium. In this talk, I will review the status and prospects for inclusive photon, di-photon, and photon+jet/multijet measurements in heavy ion collisions with the ATLAS detector at the Large Hadron Collider and with the future sPHENIX detector at the Relativistic Heavy Ion Collider.
Dennis Perepelitsa(University of Colorado Boulder)