CMS-PAS EGM-10-003
Electromagnetic Calorimeter Calibration with 7 TeV data

Abstract: The first 7 TeV LHC collisions recorded with the CMS detector have been used to perform a channel-by-channel calibration of the electromagnetic calorimeter (ECAL). Decays of π0 and η0 into two photons as well as the azimuthal symmetry of the average energy deposition at a given pseudorapidity are utilized to equalize the response of the individual channels. The ECAL comprises a central barrel section and two endcaps. Based on an integrated luminosity of up to 123 nb-1, a channel-by-channel in-situ calibration precision of 1.2% has been achieved in the barrel ECAL in the pseudorapidity region < 1. The energy scale of the ECAL has been investigated and found to agree with the simulation to within 1% in the barrel and 3% in the endcaps. The preshower detector installed in front of the endcaps has been calibrated to a precision of 2.2%.

Click here for full paper.

Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 1:
Left: Relative difference between the inter-calibration coeficients measured at the test beam and the coeficients derived from the combination of all other available measurements (laboratory, 2008 and 2009 beam dump data) versus the inter-calibration coeficients from test beam.
Right: The overall agreement is found to be about 4.6% indicating that the precision of the EE pre-calibration is about 5%.
Click image for larger png version
Click here for .eps version

  Figure 2:
Average difference from unity of the inter-calibration constants derived with the φ-symmetry method for data (solid circles) and simulation (histogram) in the crystal η index range [1, 25]. In the absence of the systematics effects described in the text, a flat distribution with statistical fluctuations around zero is expected.
Click image for larger png version
Click here for .eps version

  Figure 3:
Comparison of relative supermodule scale with φ-symmetry method between √s = 900 GeV (2009) and √s = 7 TeV (2010) data. Only statistical errors shown. The systematic uncertainty of the method is estimated to be ±0.5%.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 4:
Left: Precision of the inter-calibration constants derived from φ-symmetry as a function of ring index in EB.
Right: precision as a function of number of events for ring at crystal   index = 8.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 5:
Invariant mass distributions for photon pairs accepted by the on-line π-stream for the data and simulation in the EB (left) and in the EE (right). The distributions for data are obtained with 18.7 nb−1 . The number of events in the simulation distribution is normalized to that for the data. In addition, the difference between data and simulation observed for EB and EE energy scales with the off-line analysis (see Section 4.4) are also corrected for. Here and in the following the fitted peak width is given as a fraction of the fitted peak position.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 6:
Average number of π0 decays selected by the on-line stream and S/B as functions of the crystal η index. The η indexes of the two seed crystals from both photons forming each selected π0 → γγ candidate are used. To avoid double counting, each entry is therefore assigned a weight of 0.5. On the left, the total Monte Carlo rate is normalized to that obtained in data. The shaded bands correspond to the statistical uncertainty due to the limited size of the MC sample.
Click image for larger png version
Click here for .eps version

  Figure 7:
Measured signal rate as a function of the instantaneous luminosity shown both for the on-line calibration stream and for the events accepted by the minimum bias trigger and selected by applying the same selection cuts as those in the on-line calibration stream. For the minimum bias trigger sample, the π0 rate decreases at higher instantaneous luminosities (L > 5x1028cm-2s-1) due to the incremental prescaling of the minimum bias triggers.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 8:
π0 invariant mass reconstructed from photon pairs accepted by off-line selection for the data (left) and simulation (right). The distribution for data is obtained with 0.31 nb-1.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 9:
η → γγ invariant mass reconstructed from photon pairs passing the selection cuts for the data (left) and simulation (right).
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 10:
Left: Distribution of the inter-calibration constants in the central EB region crystal η index ≤ 45.
Right: Inter-calibration precision as a function of η-index. The expected precision estimated from simulation studies is also shown.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 11:
Distribution of the photon-pair invariant mass in the EE for data (left) and MC (right).
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 12:
Left: Comparison between the supermodule scales derived with the φ-symmetry and π0 method.
Right: Distribution of the combined inter-calibration constants in the central region crystal η-index ≤ 45.
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 13:
Energy distribution for a silicon sensor, requiring tracks with p > 1 GeV/c pointing to the preshower (left). Distribution of measured MIP values in all ES sensors having at least 1000 hits. (right)
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 14:
ES MIP values measured in CMS compared to those measured using cosmic rays in the laboratory. (left). Residuals between the in-situ MIP calibration and pre-calibration. (right)
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 15:
The calorimetric transverse energy spectrum of all the reconstructed electrons collected by the electron calibration stream, for data and simulated Minimum Bias events (left). The E/p distribution of electrons, which survive a conservative set of selections, aimed at verifying the presence of the W decay products in the stream. Data are superimposed to the Monte Carlo simulation of QCD and W→eν events (right).
Click image for larger png version
Click here for .eps version

Click image for larger png version
Click here for .eps version

Figure 16:
Energy measured by endcap crystals versus the energy deposit in ES for electrons without any identification requirement with energies measured by the combination of the silicon tracker and ECAL between 70 and 75 GeV.
Click image for larger png version
Click here for .eps version

  Figure 17:
The values of γ parameter extracted using different electron energies.

-- RiccardoParamatti - 01-Jun-2012

Edit | Attach | Watch | Print version | History: r2 < r1 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r2 - 2012-06-03 - RiccardoParamatti
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    CMSPublic All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2021 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback