Intercalibration of the CMS Electromagnetic Calorimeter Using Jet Trigger Events

This note describes a strategy for rapidly obtaining electromagnetic calorimeter crystal intercalibration at LHC start-up in the absence of test beam precalibration of the complete detector. In the case of the CMS (Compact Muon Solenoid) Electromagnetic Calorimeter, the limit on the precision to which crystals can be intercalibrated in phi using fully simulated jet trigger events, and assuming complete ignorance of the distribution of material in front of the calorimeter, is determined as a function of the pseudorapidity eta. The value of the limit has been found to be close to 1.5% in the barrel and between 3.0% and 1.0% for the fiducial region of the endcaps. The precision is limited by the inhomogeneity of tracker material. With increasing knowledge of the material distribution in the tracker, the attainable precision of the method will increase, with the potential of providing rapid and repeated calibration of the calorimeter.