Precision electromagnetic calorimetry at the energy frontier: CMS ECAL at LHC Run 2

The CMS electromagnetic calorimeter (ECAL) is a high-resolution, hermetic, and homogeneous calorimeter made of 75,848 scintillating lead tungstate crystals. After the successful quest for the Higgs boson, the CMS ECAL is at the forefront of precision measurements and the search for new physics in data from the LHC, which recently began producing collisions at the unprecedented energy of 13 TeV. The exceptional precision of the CMS ECAL, as well as its timing performance, are invaluable tools for the discovery of new physics at the LHC Run 2. The excellent performance of the ECAL relies on precise calibration maintained over time, despite severe irradiation conditions. A set of inter-calibration procedures using different physics channels is carried out at regular intervals to normalize the differences in crystal light transparency and photodetector response between channels, which can change due to accumulated radiation. In this talk we present new reconstruction algorithms and calibration strategies which aim to maintain, and even improve, the excellent performance of the CMS ECAL under the new challenging conditions of Run 2.