The CMS Calorimeter in 2007: Performance and Physics Goals

Thirteen years after the decision to build a lead tungstate based electromagnetic calorimeter for the CMS experiment at the Large Hadron Collider (LHC) at CERN the detector is now in its final assembly and installation phase for the LHC startup in early 2008. It is made of 75848 lead tungstate crystals, 61200 of 133 cubic centimeter for the barrel and 14648 of 189 cubic centimeter for the endcaps, for a total weight of 90 tons of crystals. This challenging project aims to achieve an extreme precision in photons and electrons energy measurement. General motivations, main technical challenges, measured performances, and the actual status of the project will be discussed