Measurements of the photon identification efficiency with the ATLAS detector using 4.9 fb−1 of pp collision data collected in 2011

The efficiency of the tight selection criteria used in the 2011 dataset by the ATLAS experiment to identify photons is measured using 4.9 fb−1 of pp collision data. Three in- dependent data-driven methods are used to estimate the identification efficiency in different regions of pseudorapidity η and as a function of the photon transverse momentum ET in the 15 − 300 GeV range. The three measurements give consistent results, and are combined in the overlapping ET regions into a single data-driven efficiency map. The comparison of this data-driven efficiency map with that predicted by the ATLAS simulation shows significant disagreements in some η and ET regions, where the simula- tion systematically predicts higher photon identification efficiency values. A simple data- driven correction procedure, implemented by slightly shifting the simulated electromagnetic shower shapes, restores the agreement with the data-driven values within ±5%.