CMS collaboration (2203 authors)Hollar, JonathanNayak, ArunaCalpas, BettyAlmeida, NunoBargassa, PedrameDavid Tinoco Mendes, AndreFaccioli, PietroFerreira Parracho, Pedro GuilhermeGallinaro, MicheleRodrigues Antunes, JoaoSeixas, JoaoVarela, JoaoVischia, PietroLloret Iglesias, LaraMusella, PasqualeSilva, PedroPela, JoaoLeonardo, Nuno2019-02-032019-02-032013-09-19http://dx.doi.org/10.1088/1748-0221/8/09/P09009http://hdl.handle.net/10400.26/26437The energy calibration and resolution of the electromagneticcalorimeter (ECAL) of the CMS detector have been determined usingproton-proton collision data from LHC operation in 2010 and 2011 at acentre-of-mass energy of √s = 7 TeV with integrated luminositiesof about 5\fbinv.Crucial aspects of detector operation, such as the environmentalstability, alignment, and synchronization, are presented. The in-situcalibration procedures are discussed in detail and include themaintenance of the calibration in the challenging radiationenvironment inside the CMS detector. The energy resolution forelectrons from Z-boson decays is better than 2% in the centralregion of the ECAL barrel (for pseudorapidity |η| < 0.8) and is2–5% elsewhere. The derived energy resolution for photons from125 GeV Higgs boson decays varies across the barrel from 1.1% to2.6% and from 2.2% to 5% in the endcaps. The calibration of theabsolute energy is determined from Z→e+e− decays to aprecision of 0.4% in the barrel and 0.8% in the endcaps.engjournal article2019-02-03