The IFF/EGamma has designed an improved pileup correction to the calorimeter isolation for leptons and photons. In order to use it, one needs two pileup densities (only one is used for the new correction, but the two are needed to undo the old correction) to be stored in the smart slimming list for photons and electrons (probably should be also done for muon, but this correction has not been studied in the context of muons yet). A similar improvement is expected for the neutral eflow isolation, therefore two other pileup densities are also stored. In total, four floats.
requested to merge ATLAS-EGamma/athena:AddIsoDensityToSmartSlimmingLists into 21.2