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

The Large Hadron Collider (LHC) has recently restarted operations (Run 2) with proton-proton collisions at an unprecedented centre-of-mass energy of 13 TeV and is moving to a reduced bunch spacing of 25 ns. After the successful quest for a Higgs boson via its electromagnetic decays, and the subsequent measurement of its mass, the CMS electromagnetic calorimeter (ECAL) plans to perform precision measurements and searches for new physics phenomena beyond the standard model with the data that are being collected. In this poster we present new reconstruction algorithms and calibration strategies that aim to maintain, and even improve, the excellent performance of the CMS ECAL under the new challenging experimental conditions. The CMS ECAL is a high-resolution, hermetic, and homogeneous electromagnetic calorimeter made of 75,848 scintillating lead tungstate crystals. Its resolution, as well as its timing performance, are valuable tools for the discovery of new physics with the CMS detector at the LHC. The performance of the calorimeter relies on precision calibration maintained over time, despite severe irradiation conditions. A set of intercalibration 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.