The energy scale in data is aligned to that in simulated events, while an additional smearing is applied to the reconstructed photon energy in simulation in order to reproduce the resolution observed in data, through a multistep procedure exploiting electrons from [$\cPZ\to\Pep\Pem$]{}decays.

In the ECAL barrel section, an energy resolution of about 1% is achieved for unconverted or late-converting photons, , photons converting near the inner face of the ECAL, that have energies in the range of tens of GeV. The remaining photons reconstructed in the barrel have a resolution of about 1.3% up to a pseudorapidity of $\abs{\eta} = 1$, rising to about 2.5% at $\abs{\eta} = 1.4$. In the endcaps, the resolution of unconverted or late-converting photons is about 2.5%, while the remaining endcap photons have a resolution between 3 and 4% [@CMS:EGM-14-001].

The global event reconstruction (also called particle-flow event reconstruction [@CMS-PRF-14-001]) aims to reconstruct and identify each individual particle in an event, with an optimized combination of all subdetector information. In this process, the identification of the particle type (photon, electron, muon, charged hadron, neutral hadron) plays an important role in the determination of the particle direction and energy. Photons (, coming from  decays or from 