CMS electromagnetic calorimeter calibration and timing performance during LHC Run I and future prospects

The CMS ECAL is a high-resolution, hermetic, and homogeneous electromagnetic calorimeter made of 75,848 scintillating lead tungstate crystals. It relies on precision calibration as well as a stable timing measurement to achieve and maintain its design performance. A set of inter-calibration procedures, in particular utilizing different physics channels, is carried out to normalize the differences in crystal light yield and photodetector response between channels. The timing precision achieved is used in important physics measurements and also allows the study of subtle calorimetric effects, such as the timing response of different crystals belonging to the same electromagnetic shower. The challenges of the different calibration techniques and the performance evolution during LHC Run I, as well as the timing resolution achieved in beam tests and during Run I, will be presented. The impact of the calibration and timing precision on physics is illustrated through the successful quest for the Higgs boson via its electromagnetic decays, and the subsequent mass measurement of the newly discovered particle. Conclusions are drawn for the performance to be expected from 2015 onwards, following the start of the LHC Run II. In addition, we present prospects for the high luminosity phase of the LHC