The electromagnetic calorimeter of CMS, summary and status

The construction of the lead tungstate crystal calorimeter for the CMS experiment at the Large Hadron Collider (LHC) is close to completion. The barrel part of the calorimeter composed of 61200 crystals is installed and operated inside CMS. Only 102 readout channels are problematic including the 21 entirely dead, corresponding to 0.17 % and 0.034 %, respectively. All 14648 end-cap crystals are mounted. The electronics installation and commissioning of one end-cap has finished and the second will be finished in few weeks. The construction of the pre-shower detectors installed in front of the end-caps is well advanced. The many challenges of the design and construction imposed by a 4 Tesla magnetic field, radiation levels ranging from 100 krad up to several Mrad and a bunch crossing rate of 40 MHz were mastered by a huge effort in developing and testing appropriate crystals, photo-detectors and readout electronics carried out over the past ~ 15 years. Test beam results demonstrate that the energy resolution obtained is better than 0.5 % at high energies. All readout channels in the barrel are inter-calibrated to better than 2% using cosmic muons.