Prompt photons are a powerful tool to study heavy ion collisions. Their
production rates provide access to the initial state parton distribution
functions and also provide a means to calibrate the expected energy of jets
that are produced in the medium. The ATLAS detector measures photons with its
hermetic, longitudinally segmented calorimeter, which gives excellent spatial
and energy resolutions, and detailed information about the shower shape of each
measured photon. This provides significant rejection against the expected
background from the decays of neutral pions in jets. Rejection against jet
fragmentation products is further enhanced by requiring candidate photons to be
isolated. First results on the spectra of isolated prompt photons from a
dataset with an integrated luminosity of approximately 0.13 nb^-1 of lead-lead
collisions at sqrt(s_NN)=2.76 TeV are shown as a function of transverse
momentum and centrality. The measured spectra are compared to expectations from
perturbative QCD calculations.Comment: Proceedings for Hard Probes 2012, May 27 - June 1, 2012, Cagliari,
Sardinia, Ital
