Calibration of the Electromagnetic Calorimeter of CMS

The electromagnetic calorimeter (ECAL) of the CMS experiment, that will take data at LHC, has been designed to get an excellent energy resolution, essential to search for di-photonic resonances. ECAL is made of lead tungstate crystals whose individual response depends on several contributions and this variation affects the resolution of the whole detector. Hence, a channel to channel intercalibration is required to get the goal performances. The calibration of the detector at the start-up, the in-situ calibration strategies and their commissioning with first data will be reported. CMS-NOTE-2008-018 Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up CMS-NOTE-2006-021 Inter-Calibration of the CMS Electromagnetic Calorimeter with Isolated Electrons