The CMS Lead Tungstate Electromagnetic Calorimeter

The CERN LHC will open a new regime in the exploration of fundamental interactions. Of central importance to these studies will be the precise measurement of high energy electrons and photons. The CMS experiment therefore incorporates a high resolution electromagnetic calorimeter comprising 76000 lead tungstate crystals, covering almost 4pi, and capable of operating reliably for ten years in a very hostile environment. The detector design is presented, together with beam measurements demonstrating that the goal for energy resolution of better than 0.5% above 100 GeV can be achieved.