The performance is presented of the reconstruction and identification
algorithms for electrons and photons with the CMS experiment at the LHC.
The reported results are based on proton-proton collision data collected
at a center-of-mass energy of 13 TeV and recorded in 2016-2018,
corresponding to an integrated luminosity of 136 fb(-1). Results
obtained from lead-lead collision data collected at root S-NN = 5.02 TeV
are also presented. Innovative techniques are used to reconstruct the
electron and photon signals in the detector and to optimize the energy
resolution. Events with electrons and photons in the final state are
used to measure the energy resolution and energy scale uncertainty in
the recorded events. The measured energy resolution for electrons
produced in Z boson decays in proton-proton collision data ranges from 2
to 5%, depending on electron pseudorapidity and energy loss through
bremsstrahlung in the detector material. The energy scale in the same
range of energies is measured with an uncertainty smaller than 0.1
(0.3)% in the barrel (endcap) region in proton-proton collisions and
better than 1(3)% in the barrel (endcap) region in heavy ion
collisions. The timing resolution for electrons from Z boson decays with
the full 2016-2018 proton-proton collision data set is measured to be
200 ps