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The CMS crystal calorimeter

The measurement of the energy of electrons and photons with very high accuracy is of primary importance for the study of many physics processes at the large hadron collider (LHC), in particular for the search of the Higgs boson. The CMS experiment uses a crystal calorimeter with pointing geometry, almost covering 4p, as it offers a very good energy resolution. It is divided into a barrel composed of 61200 lead tungstate crystals, two end-caps with 14648 crystals and a pre-shower detector in front of the end-cap. The challenges of the calorimeter design arise from the high radiation environment, the 4 Tesla magnetic field, the high bunch crossing rate of 40 MHz and the large dynamic range, requiring the development of fast, radiation hard crystals, photo-detectors and readout electronics. An overview of the construction and design of the calorimeter is presented, with emphasis on some of the details required to meet the demanding performance goals.