Performance of the CMS Electromagnetic Calorimeter in LHC Run2

Abstract

Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high resolution electron and photon energy measurements, which are provided by the electromagnetic calorimeter (ECAL). During the Run II at the LHC it has been operating with proton-proton collisions at 13 TeV center-of-mass energy, 25 ns bunch spacing, and an unprecedented instantaneous luminosity. High pileup levels (simultaneous collisions) and the ageing of crystals from exposure to large particle fluences necessitate a retuning of the ECAL readout, trigger thresholds, and reconstruction algorithms, to maintain the best possible performance in these increasingly challenging conditions. In addition, the energy response of the detector must be precisely calibrated and monitored using the expected response of the detector in physics events as well as using dedicated monitoring hardware. This work presents the new reconstruction algorithm and calibration strategies that have been implemented at CMS and the excellent performance achieved by the ECAL during Run II.