Centrality, rapidity and $p_T$ dependence of isolated prompt photon production in lead-lead collisions at $\sqrt{s_{NN}}$ = 2.76 TeV with the ATLAS detector at the LHC

The ATLAS experiment at the LHC has measured prompt photon production in $\energy$ Pb+Pb collisions using data collected in 2011 with an integrated luminosity of 0.14 $\mathrm{nb}^{-1}$. The measurement is performed with a hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the shower shape of each measured photon. A multiparameter selection on a set of nine shower properties, coupled with an isolation criterion based on the energy deposited in the cone around a photon, gives measured purities ranging from 50% at low $p_T$ to greater than 90% at high $p_T$. Photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality, pseudorapidity (in two intervals $|\eta|<1.37$ and $1.52<|\eta|<2.37$) and transverse momentum (from $22 < $p_T$ < 280$ GeV). The scaled yields are compared to expectations from JETPHOX (perturbative QCD calculations at next to leading order), as are the ratios of the forward yields to those near mid-rapidity. The observed photon yields agree well with the predictions, but the ratios of yields at forward rapidity to the yields near mid-rapidity are systematically closer to calculations incorporating the correct isospin of the colliding system.