Calibration and Performance of the CMS Electromagnetic Calorimeter During LHC Run 3

The electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid (CMS) experiment at the Conseil Européen pour la Recherche Nucléaire [European Organization for Nuclear Research (CERN)] Large Hadron Collider (LHC) is crucial for many physics analyses, ranging from Higgs measurements to searches for new physics. Precise calibration of the detector and all its individual channels is essential to achieve the best possible resolution for electron and photon energy measurements. Additionally, calibration is important for measuring the electromagnetic component of jets and for contributing to energy sums that provide information about particles that leave no signal in the detectors, such as neutrinos. To ensure the stability of the energy response over time, a laser monitoring system is employed to measure radiation-induced changes in the detector hardware and compensate for them during reconstruction. A dedicated calibration of each detector channel is also performed using physics events, exploiting electrons from W and Z boson decays, photons from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi ^{0}$ </tex-math></inline-formula> decays, and the azimuthally symmetric energy distribution of minimum bias events. This article will summarize the techniques used for ECAL energy and time calibrations and will discuss a new system developed to automatically execute the calibration workflows during data taking for LHC Run 3. The ECAL performance achieved during the reprocessing of data collected by CMS in 2022 and 2023 will also be discussed.