In-situ Calibration of the CMS Electromagnetic Calorimeter

The CMS electromagnetic calorimeter is a key instrument to exploit the energy frontier represented by LHC, expected to deliver proton-proton collisions at a centre-of-mass energy of 14 TeV. High performance of the ECAL, in particular precise energy measurement of electrons and protons, will enhance the discovery potential of CMS. In-situ calibration with physics events will be the main tool to minimize the constant term in the resolution function. The calibration strategies and the studies performed on simulated data to achieve this goal are presented.