CMS-DP-2013/007
2012 ECAL detector performance plots

Abstract: Collection of plots summarizing the ECAL performance on 2012 data. General update of 2011 performance plots available in CMS-DP-2012/007, CMS-DP-2012/015, CMS-DP-2012/026, CMS-DP-2012/027

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Figure	Caption
pdf version	ECAL barrel APD dark current Dark current evolution of the Avalanche Photodiodes installed in the ECAL Barrel (2 APDs are installed on each crystal) • 50 channels (=100 APDs) are connected to one HV channel • The APDs are operated at gain 50 and are kept at 18°C • The plot shows the average dark current measured per channel as a function of time. The colours indicate different eta regions of the ECAL barrel • APDs are silicon devices and they are sensitive to neutron damage. The neutrons create defects in the silicon lattice, which cause an increase in the dark current. The neutron fluence at high eta is expected to be larger by a factor of 2 with respect to the central barrel (eta=0), and the measured current is observed to scale accordingly. • The plot also shows in red the delivered luminosity as a function of time. • During technical stops and winter shutdowns a part of the APD defects anneals and the current reduces. The short time component of the annealing is of about 20 days.
pdf version pdf version	Noise evolution of the APD signal in EB Single channel noise measured on the pre-samples of the laser events taken during standard monitoring sequences in 2011 and 2012 • X axis : time; Y axis : noise amplitude • Top plot: in ADC counts. Bottom plot : in MeV • Colours: various eta from 0 to 1.5 (see palette) • Right plot obtained from left one by applying the ADC2GeV factor, intercalibration and correcting for response changes.
pdf version pdf version	Noise evolution of the VPT signal in EE Single channel noise measured on the pre-samples of the laser events taken during standard monitoring sequences in 2011 and 2012 • X axis : time; Y axis : noise amplitude • Top plot: in ADC counts. Bottom plot : in MeV • Colours: various eta from 1.5 to 2.8 (see palette) • Right plot obtained from left one by applying the ADC2GeV factor, intercalibration and correcting for response changes.
pdf version pdf version	ECAL trigger performance Level 1 electron trigger performance L1 EG20 trigger efficiency vs offline electron supercluster ET • The plot shows the trigger efficiency for 2012 data, measured using a Tag and Probe method on Zee events. • The table shows the transverse energy for which the trigger is 50%, 95% and 99% efficient in the EB and EE, and the efficiency at 100 GeV which corresponds roughly to the plateau efficiency. • In the endcaps, response changes are corrected at the ECAL towers level. The RCT calibration is modified accordingly and includes a correction for the energy loss in the pre-shower. • Data : April-September 2012, 12.0 fb-1 • Method : Z→e+e- events selected by Tag&Probe • ET(tag) > 20 GeV; ET(probe) > 5 GeV • WP80; 60 < mee < 120 GeV; Tag triggers EG20. Match electron to L1 candidate in RCT region containing its highest TT energy deposit. • Efficiency = fraction of probes triggering. • Unbinned fit using an integrated crystal ball function: convolution of resolution and step function.
pdf version	History of relative response Relative response to laser light (440 nm in 2011 and 447 nm in 2012) measured by the ECAL laser monitoring system, averaged over all crystals in bins of pseudorapidity, for the 2011 and 2012 data taking periods The response change observed in the ECAL channels is of the order of a few percent in the barrel, while it reaches up to 25% in the most forward endcap regions used for electron and photon reconstruction. The response change observed in the ECAL channels is up to 6% in the barrel and it reaches up to 30% at η ~ 2.5, the limit of the tracker acceptance. The response change is up to 70% in the region closest to the beam pipe. These measurements are used to correct the physics data. This is an update of the plots appearing in CMS-DP-2012/007 and CMS-DP2012/015, and includes measurements taken up to December, 17th 2012. The bottom plot shows the instantaneous LHC luminosity delivered during this time period.
pdf version	Relative response Relative response to laser light (440 nm) measured by the ECAL laser monitoring system, averaged over all barrel crystals, for some LHC fills in 2011. The response loss observed in a fill and the corresponding recovery in the interfill time are clearly visible. These measurements are used to correct the physics data.
pdf version pdf version pdf version pdf version	2012 inter-calibration • Precision of channel inter-calibration, using energy deposits, as a function of pseudo-rapidity in the ECAL barrel (two top plots) and endcap (two bottom plots) detectors. • The precision for measuring the inter-calibration constants from φ-symmetry, from π0→γγ and η→γγ decays, and from W and Z decay electrons, is shown as a function of η in EB and EE, using 2012 data. The precision of the phi-symmetry and photon calibrations is at the level of the systematic errors. The precision of the electron calibration is still dominated by the statistical errors for η > 1. • The black points represent the precision of the combination of the three methods (weighted average). • References: CMS PAS EGM-10-003 and CMS PAS EGM-11-001.
pdf version pdf version	E/p history History plot for 2012 data of the ratio of electron energy E,measured in the ECAL Barrel (ECAL Endcap), to the electron momentum p, measured in the tracker: • the dataset corresponds to the reconstruction with the latest calibration and alignment conditions (Winter2013 re-reconstruction); • the electrons are selected from W→eν decays. Each point in the plot is computed from 20000 (10000) selected W→eν events with the reconstructed electron located in the ECAL Barrel (ECAL Endcap); • the E/p distribution for each point is fitted to a template E/p distribution measured from data (using the entire 2012 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 variations due to transparency loss are applied; • A stable energy scale is achieved throughout 2012 run after applying laser corrections: • ECAL Barrel: average signal loss ~5%, RMS stability after corrections 0.09% • ECAL Endcap: average signal loss ~18%, RMS stability after corrections 0.28%.
pdf version pdf version	ECAL energy calibration The two plots show the impact on the Z→e+e- 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 channel response loss.
pdf version pdf version	ECAL supercluster energy The two plots show the impact on the Z→e+e− energy scale and resolution from the incorporation of more sophisticated clustering and cluster correction algorithms.
pdf version pdf version	Experimental Zee invariant mass The mass resolution of the Z peak, reconstructed from its di-electron decay mode, as a function of time for the barrel and the endcaps. The width of the Z peak is fitted with a convolution of a Crystal Ball with a Breit-Wigner line shape. The Gaussian width parameter of the Crystal Ball function is taken as a measure of the mass resolution.
pdf version pdf version	ECAL energy resolution with Zee Relative electron (ECAL) energy resolution unfolded in bins of pseudo-rapidity η for the barrel and the endcaps. Electrons from Z→ee decays are used. The resolution is shown separately for low bremsstrahlung electrons (R9>0.94 with R9 = E3x3 / ESC) and for the inclusive sample. The resolution σE/E is extracted from an unbinned likelihood fit to Z→ee events, using a Voigtian (Landau convoluted with Gaussian) as the signal model. The resolution is plotted separately for data and MC events. • Conclusions: • The resolution is affected by the amount of material in front of the ECAL and is degraded in the vicinity of the eta cracks between ECAL modules (indicated by the vertical lines in the plot) • The resolution, especially in the endcaps, improves significantly after a dedicated calibration using the full 2012 CMS dataset (blue points) with respect to the prompt calibration from early 2012 CMS data (gray points).