Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collisions at √s = 7 TeV

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Pálinkás, József and Karancsi, János and Trócsányi, Zoltán and Ujvári, Balázs and Krajczár, Krisztián and Veres, Gábor (2013) Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collisions at √s = 7 TeV. JOURNAL OF INSTRUMENTATION, 8 (9). ISSN 1748-0221

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Abstract

The energy calibration and resolution of the electromagnetic calorimeter (ECAL) of the CMS detector have been determined using proton-proton collision data from LHC operation in 2010 and 2011 at a centre-of-mass energy of √ s = 7 TeV with integrated luminosities of about 5 fb−1 . Crucial aspects of detector operation, such as the environmental stability, alignment, and synchronization, are presented. The in-situ calibration procedures are discussed in detail and include the maintenance of the calibration in the challenging radiation environment inside the CMS detector. The energy resolution for electrons from Z-boson decays is better than 2% in the central region of the ECAL barrel (for pseudorapidity |η| < 0.8) and is 2–5% elsewhere. The derived energy resolution for photons from 125 GeV Higgs boson decays varies across the barrel from 1.1% to 2.6% and from 2.2% to 5% in the endcaps. The calibration of the absolute energy is determined from Z → e +e − decays to a precision of 0.4% in the barrel and 0.8% in the endcaps.

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