A tool for $\gamma/\pi^0$ separation at high energies

This note describes a tool developed to distinguish between neutral pions that are reconstructed as a single cluster in the LHCb ECAL and photons. The separation is based on the different shape of electromagnetic clusters produced by these two particles. The tool allows to select high energy photons with 95% efficiency, while rejecting about half of the background from neutral pions. Methods to calibrate the efficiency of the tool in real data and to deal with the different performance in Monte Carlo samples are also presented.