Centrality, rapidity and ${p_{\mathrm{T}}}$ 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 $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV 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 $p_{\mathrm{T}}$ to greater than 90% at high $p_{\mathrm{T}}$. 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 $22 < p_{\mathrm{T}} < 280$ 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 for proton-proton within statistical and systematic uncertainties. Both the yields and ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei, and another which includes the EPS09 nuclear modifications to the proton parton distribution functions.