Electron-based longitudinal weights for the ATLAS EM Barrel Calorimeter and shower isolation studies with an application to the $H \ra ZZ^{(*)} \ra 4e$ analysis

In this note a full electron-based calibration of the Electromagnetic Barrel Calorimeter is performed. The improvement in resolution and linearity for electrons of energies ranging from 10 GeV up to the TeV scale is demostrated. A new general method is proposed which can be applied in multi-lepton final states where detector level information is exploited to discriminate between signal and background. The method is applied to the H->ZZ(*)->4e channel.