The CMS Electromagnetic Calorimeter Pre-calibration with Cosmic Rays and Test Beam Electrons

The electromagnetic calorimeter of the CMS experiment at the new CERN proton-proton Collider (LHC) is at an advanced stage of construction. A necessary condition for its optimal performance is a precise channel-to-channel calibration. The use of cosmic rays allows the pre-calibration of all the channels at the level of 2% before the final installation in CMS and provides an extensive functionality test, essential for the commissioning of the detector. On the other hand, a beam of electrons permits extremely precise (better than 0.5%) pre-calibration coefficients to be obtained on a fraction of the calorimeter, that can also be used as a reference for the in situ calibration procedures that will rely on physics data.