CMS-DP-2012/002
ECAL Performance Results on 2011 data

Abstract: Performance plots on energy calibration and resolution of the CMS Electromagnetic calorimeter, based on the 2011 pp data sample.

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Figure	Caption
pdf version	History plot for 2011 data of the ratio of electron energy E, measured in the ECAL Barrel, to the electron momentum p, measured in the tracker The electrons are selected from W->enu decays. Each point in the plot is computed from 12000 selected W->enu events with the reconstructed electron located in the ECAL Barrel. The E/p distribution for each point is fitted to a template E/p distribution measured from data (using the entire 2011 dataset) in order to provide a relative scale for the E/p measurement versus time. The history plots are shown before (red points) and after (green points) corrections to ECAL crystal response due to transparency loss are applied. The magnitude of the average transparency correction for each point (averaged over all crystals in the reconstructed electromagnetic clusters) is indicated by the continuous blue line. A stable energy scale is achieved throughout the 2011 run after applying transparency corrections to the ECAL data. The average signal loss of 2.5% in the ECAL barrel is corrected with an RMS stability of 0.14% Plot upload: 02 Mar 2012, Plot contact: Andrea.Benaglia@cernSPAMNOT.ch
pdf version	Z->ee invariant mass plot for 2011 data, from the reconstruction of di-electron events with both electrons in the ECAL Barrel The plot includes only electrons with low energy loss through bremsstrahlung in the CMS tracker. The plot shows the improvements in Z->ee energy scale and resolution that are obtained from applying energy scale corrections to account for the intrinsic spread in crystal and photo-detector response, and time-dependent corrections to compensate for crystal transparency loss. The former are determined using three independent methods: in-situ phi-symmetry, beam-induced muon data, and di-photon invariant mass plots from pi0 and eta decays. The latter are measured using laser monitoring data, which is recorded in the LHC abort gaps during physics data taking. The position of the peak of the Z->ee invariant mass plot in data is used to calibrate the overall energy scale of the calorimeter. The instrumental resolution (width of the Crystal Ball function convoluted to the Z->e+e- invariant mass lineshape) after preliminary energy calibration of 2011 data is measured to be 1.0 GeV in the ECAL Barrel Plot upload: 02 Mar 2012, Plot contact: Shervin.Nourbakhsh@cernSPAMNOT.ch