Measurement of high-pT isolated prompt photons in lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector at the LHC

Prompt photons are a powerful tool in heavy ion collisions. Their production rates provide access to the initial state PDFs, which are expected to be modified by nuclear effects. They also provide a means to calibrate the expected energy of jets that are produced in the medium, and thus are a tool to probe the physics of jet quenching more precisely both through jet spectra and fragmentation properties. The ATLAS detector measures photons with its hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the shower shape of each measured photon. This gives significant rejection against the expected background from neutral pions in jets. Rejection against jet fragmentation products is further enhanced by isolation criteria, which can be based on calorimeter energy or the presence of high pT tracks. First results on the spectra of isolated prompt photons from approximately 133 µb-1 of lead-lead data are shown, as a function of transverse momentum and centrality. The measured spectra are compared to expectations from perturbative QCD calculations