CMS NOTE 2010/012 (CMS-PAS EGM-10-002)
Electromagnetic Calorimeter Commissioning and First Results with 7 TeV data

Abstract: The operation and general performance of the CMS electromagnetic calorimeter at √s= 7 TeV are described. The first LHC beams have been used to finalize the commissioning of ECAL readout and trigger and to verify the readiness of ECAL for data taking.

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  Figure 1:
Graphical representation of the barrel ECAL (EB) showing the fully working areas (green) and few problematic channels. The percentage of fully operational channels in the EB is 99.30%.
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  Figure 2:
Graphical representation of the endcap ECAL (EE) showing the fully working areas (green) and few problematic channels. The percentage of fully operational channels in the EE is 98.94%.
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Figure 3:
Left shows the temperature stability, represented by the rms of the measurements of each thermistor over two months.
Right shows the measured signal stability over two weeks, represented by the ratio of signals from the APD and the PN diode when illuminated by the blue laser.
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  Figure 4:
Graphical representation of the four ES planes, showing the dead sensors (white squares) and noisy strips (red strips). The percentage of fully operational channels in the ES is 99.79%.
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Figure 5:
Mean time per EB/EE crystal hit after alignment of the online PLL readout phase alone (dashed) and the improvement of also including the offline time calibration from 2009 beam splashes (full).
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Figure 6:
Mean reconstructed time for groups of 360 crystals belonging to rings at constant η, as a function of pseudo-rapidity (left) and for all rings (right). The collisions-obtained offline time alignments are applied in both cases.
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  Figure 7:
Synchronization of the relative phase between Preshower readout electronics (at the level of “ladders”) and the passage of particles through the sensors, before and after fine tuning.
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Figure 8:
Left: Bunch-crossing (BX) assignment efficiency as a function of the time-setting used.
Right: comparison between the online (TCC-computed) trigger primitives and offline measurements of the transverse energies contained in the towers. The plateau at TP = 64 GeV corresponds to the maximum hardware value.
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Figure 9:
(a) Distribution of the “Swiss Cross” topological variable (1− E4/E1) for the highest energy deposit in each event for data and simulation (√s = 7 TeV). Only events with an energy deposit with ET > 3 GeV are plotted. The two distributions are normalized to the same total number of minimum bias events, before the cut on the signal transverse energy is applied;
(b) Reconstructed time corresponding to the maximum of the signal pulse for the highest energy deposit in each event (with ET > 3 GeV). The dashed histogram indicates non-isolated energy deposits that satisfy (1 − E4/E1) < 0.95.
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Figure 10:
Energy spectra of the individual channels in the barrel (left) and in the endcaps (right) from 7 TeV minimum bias collision events.
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  Figure 11:
Energy spectra of the strips in the preshower from 7 TeV minimum bias collision events. The bump at high energy is due to signal saturation in High Gain mode.
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  Figure 12:
Pseudo-rapidity distributions of the channel with the highest reconstructed energy in 7 TeV minimum bias collision events for EB.
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Figure 13:
Pseudo-rapidity distributions of the channel with the highest reconstructed energy from 7 TeV minimum bias collision events for EE- (left) and EE+ (right).
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Figure 14:
Azimuthal distribution of the channel in ECAL barrel (left) and ECAL endcaps (right) with the highest reconstructed energy from 7 TeV minimum bias collision events.
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Figure 15:
Preshower occupancy as functions of pseudo-rapidity (left, averaged over all φ) and azimuthal angle (right, averaged over all η
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Figure 16:
Comparison between data and simulation for the total cluster energies measured by each plane of the ES, expressed in units of MIP, as well as the ratio between the energies.
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  Figure 17:
Correspondence between the energy measured in EE basic clusters and the weighted ES energy for electrons with energies between 70 and 75 GeV. For the data, one point represents a single electron, whilst for the MC we use a profile plot due to the larger available statistics.
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Figure 18:
Transverse energy spectra for EB (left) and EE (right) superclusters from 7 TeV minimum bias collision events.
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Figure 19:
Gaussian width of the time difference between two neighbouring crystals as a function of the variable AeffN, for EB (left) and EE (right). The fitted curves are shown as continuous lines. Energies range, respectively, up to 4.5 GeV and 18 GeV.
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  Figure 20:
Residual measurements between Tracker and each of the ES planes, before and after software alignment.
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  Figure 21:
Alignment between ES and EE for each ES plane, for both data and MC. The “out of the box” alignment is better than a millimetre.
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Figure 22:
Alignment between Tracker and EE+ (left) and EE- (right) before and after software re-alignment.
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Figure 23:
Preshower signal to noise ratio for single particles (left) and matching efficiency (right). The matching efficiency decreases for low pT due to multiple scattering, whilst the plateau is not at 100% due to fake tracks etc.
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Figure 24:
Resolution of the γγ invariant mass as a function of η (top) and pT (bottom) of the γγ pair. For the top plot we have used mainly low pT information. In the lower plot we include plots of the simulated mass resolution obtained when using either the MC true energy or MC true angle, to determine the dominant factors.

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  Figure 25:
Mass spectrum of reconstructed pairs of photons showing a clear peak corresponding to the π0 mass.
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Figure 26:
Stability of the measurement of the π0 mass peak in the barrel ECAL. Left plot shows the mass peak as a function of run number, whilst the right plot is the projection, showing an RMS variation of around 0.18%

-- RiccardoParamatti - 01-Jun-2012

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Topic revision: r2 - 2012-06-03 - RiccardoParamatti
 
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