Abstract: CMS ECAL , calibration and performance in 2018 ultra legacy rereconstruction.
Figure  Caption 

Examples of the invariant mass of photon pairs with one photon depositing a fraction of its energy in a crystal of the ECAL Barrel at η = 0.03 (top), and of the ECAL Endcap at η = 1.83 (bottom), in the mass range of the π0. A subset of the data collected in 2018 is used, corresponding to half of the total dataset. These events are collected by CMS with a dedicated trigger at a rate of 7 (2) kHz in the Barrel (Endcaps). The high trigger rate is made possible by a special clustering algorithm that saves only a minimal amount of information of the events, in particular, energy deposits in the ECAL crystals surrounding a possible π0 candidate. For candidates in the Endcaps, the determination of the photon position in the region with 1.7 <abs(η)< 2.55 is improved by the presence of the Preshower, which results in a better mass resolution. These events are used as prompt feedback to monitor the effectiveness of the laser monitoring calibration and to intercalibrate the energy of ECAL crystals. The π0 mass is shown before the crystal intercalibration. 

Time stability of the dielectron invariant mass distribution for the 2018 data taking period using Z→ee electrons. The plot shows the time stability of the median dielectron invariant mass with a refined recalibration performed in 2019 for the full 2018 dataset. Both electrons are required to be in the ECAL Barrel (left) or in the ECAL Endcaps (right). Each time bin has around 10,000 events. The error bar on the points denotes the statistical uncertainty on the median, which is evaluated as the central 95% interval of medians obtained from 200 "bootstrap" resamplings. The right panel shows the distribution of the medians. At the analysis level, residual drifts in the energy scale with time are corrected for in approximately 18hour intervals corresponding to at most one LHC fill. 

Stability of the shower shape of the electromagnetic deposits in the ECAL for leading electrons from Z decays. The plot shows the time stability of the shower shape of the leading electron from Z decays with a refined recalibration performed in 2019. The event selection requires two electrons to be in the ECAL Barrel (left) or in the ECAL Endcaps (right). Each time bin has around 10,000 events. The error bar on the points denotes the statistical uncertainty on the median, which is evaluated as the central 95% interval of medians obtained from 200 "bootstrap" resamplings. The right panel shows the distribution of the medians. The shower shape is measured by the variable R9, defined as the ratio of the energy deposit in the 3x3 crystal matrix around the seed crystal to that in the supercluster. R9 is responsive to changes in pedestal and noise.


Dielectron invariant mass distribution for the 2018 data taking period using Z→ee electrons. The plot shows the dielectron invariant mass distribution for Z decay events with two calibration sets for the full 2018 dataset: the “preliminary” autumn 2018 calibration (RED) and a “refined” recalibration performed in 2019 (GREEN). While for the refined calibration a complete recalibration of the crystals was performed, for the preliminary calibration only timedependent effects for the first part of the dataset were accounted for. Both electrons are required to be in the ECAL Barrel (left) or in the ECAL Endcaps (right). The relative resolutions are quoted in the legend, defined as the ratio of σ (Gaussian standard deviation of the Gaussian that is convoluted with a BreitWigner as the signal model (Voigtian fit)) to μ (mean). Events used in the calibration are excluded from the fit. 

Dielectron invariant mass distribution for the 2018 data taking period using Z→ee lowbremsstrahlung electrons. The plot shows the dielectron invariant mass distribution for Z decay events with two calibration sets for the full 2018 dataset: the “preliminary” autumn 2018 calibration (RED) and a “refined” recalibration performed in 2019 (GREEN). While for the refined calibration a complete recalibration of the crystals was performed, for the preliminary calibration only timedependent effects for the first part of the dataset were accounted for. Both electrons are required to be in the ECAL Barrel (left) or in the ECAL Endcaps (right) and to have low bremsstrahlung. The relative resolutions are quoted in the legend, defined as the ratio of σ (Gaussian standard deviation of the Gaussian that is convoluted with a BreitWigner as the signal model (Voigtian fit)) to μ (mean). Events used in the calibration are excluded from the fit. Refined calibration fitted resolution values (1.4% and 2.7% for EB and EE, respectively)are consistent with those obtained in the final SuperCluster unfolded resolution results (~2%(/sqrt(2)) and ~4%(/sqrt(2)) for EB and EE, respectively.) 

Dielectron invariant mass distribution for the 2018 data taking period using Z→ee highbremsstrahlung electrons. The plot shows the dielectron invariant mass distribution for Z decay events with two calibration sets for the full 2018 dataset: the “preliminary” autumn 2018 calibration (RED) and a “refined” recalibration performed in 2019 (GREEN). While for the refined calibration a complete recalibration of the crystals was performed, for the preliminary calibration only timedependent effects for the first part of the dataset were accounted for. Both electrons are required to be in the ECAL Barrel (left) or in the ECAL Endcaps (right) and to have high bremsstrahlung. The relative resolutions are quoted in the legend, defined as the ratio of σ (Gaussian standard deviation of the Gaussian that is convoluted with a BreitWigner as the signal model (Voigtian fit)) to μ (mean). Events used in the calibration are excluded from the fit. 

ECAL energy resolution with Zee in 2018 data Relative electron (ECAL) energy resolution unfolded in bins of pseudorapidity η for the ECAL Barrel and the ECAL Endcaps. Electrons from Z→ee decays are used. The resolution is shown separately for low bremsstrahlung electrons and for all electrons (“inclusive”). The resolution is measured on 2018 data. The relative resolution σE/E is extracted from an unbinned likelihood fit to Z→ee events, using a Voigtian (BreitWigner convoluted with Gaussian) as the signal model. 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 last point of the preliminary calibration is out of the yaxis scale of the plot • The resolution improves significantly after a refined calibration using the full 2018 dataset with respect to a preliminary calibration for which only time dependent effects in the first part of the dataset were corrected for 

pdf version 
2018 intercalibration precision Residual miscalibration of the ECAL channel intercalibration, as a function of pseudorapidity with the dataset recorded during 2018. The red, blue, and green points represent the residual miscalibration of the intercalibration constants (IC) obtained with three different methods, and the black points represent the residual miscalibration of the combination of the three methods. The red points refer to the IC obtained with electrons from Z→ee decays using the known Z mass as energy reference. The blue points refer to IC obtained with electrons from W and Z decays using the tracker momentum as energy reference. The green points refer to IC obtained using photons from π0→γγ decays. Such decays are used only for abs(η)<2 due to the low signal over noise ratio otherwise. The IC combination is performed by weighting the different methods relatively to energy resolution performance as measured in Z→ee decays. Between 2<abs(η)<2.5, the E/p point used for combination is out of the yaxis scale of the plot. No combination is performed for abs(η)>2.5, where only Z→ee decays are used. 
pdf version 
The two planes of the Preshower (ES), coupled with the EE crystals, form a sampling calorimeter. The ES essentially counts the number of charged particles passing through the layers of silicon, which is an estimate of the amount of energy deposited in the ES lead absorbers. We use charged particles with momentum nearly close to minimum ionizing to calibrate the ES, so for simplicity we refer to them as “MIPs”. They are collected with the Preshower operated in highgain mode. The designgoal accuracy of the channelbychannel calibration is set to 5%. This corresponds to a contribution of about 0.25% to the overall EE+ES energy resolution for highenergy electrons since only a few percent of electron/photon energy is deposited in ES. The sources of response variation (sensortosensor and channeltochannel) are the sensor thickness seen by the incident particles (depends on angle of incidence), gain of the frontend electronics chain, and charge collection efficiency which varies with the radiation damage.
The plot shows the decreasing of MIP response with regard to the 2015 calibration (from 2015B to the end of 2018D) in 5 eta regions (the interval in eta is 0.2) of the front plane. The xcoordinate of each data point represents the integrated luminosity at which the MIP calibration was done. The calibration was performed every 1020 fb1. The decreasing rate on ES+ is similar to one on ES, thus the averages of those rates are used. In general, the MIP responses decrease as a function of luminosity. The only exception is in the beginning of 2017 data taking, when the bias voltage was increased by 80 Volts The MIP response decreases faster in the higher eta region. This result implies that the ES sensors in high eta regions are more affected by the radiation damage. 
pdf version 
The plot shows the decreasing of MIP response with regard to the 2015 calibration (from 2015B to the end of 2018D) in 5 eta regions (the interval in eta is 0.2) of the rear plane. The xcoordinate of each data point represents the integrated luminosity at which the MIP calibration was done. The calibration was performed every 1020 fb1. The decreasing rate on ES+ is similar to one on ES, thus the averages of those rates are used. In general, the MIP responses decrease as a function of luminosity. The only exception is in the beginning of 2017 data taking, when the bias voltage was increased by 80 Volts The MIP response decreases faster in the higher eta region. This result implies that the ES sensors in high eta regions are more affected by the radiation damage 
pdf version 
Due to radiation damage, the Preshower response decreases with time. A data/MC correction on the runs between 2 successive calibrations to stabilize the recorded energy is applied. The correction was computed by minimizing the χ2 value between the energy distribution of data and MC. The plot shows the calibrated deposited energy of electrons measured with the Preshower planes at low gain as a function of integrated luminosity before (BLACK) and after (BLUE) applying the correction factor. It also displays the comparison to the MC prediction (RED). Four different data/MC correction factors are applied in this plot. They are calculated for subperiods in a period between two consecutive high gain calibrations of an integrated luminosity of 9.7 fb1. The 4 subperiods are separated with vertical lines (GREEN). The High gain calibration, normalized to low gain by a factor of 1/6, is applied to the data points in black. Then for each subperiod, a data/MC correction factor is derived and applied at the middle of the interval, generating a slight over correction in the beginning of the intervals. Applying the data/MC correction to the data between two ES calibrations, improves the stability of the energy measurement.

I  Attachment  History  Action  Size  Date  Who  Comment 

png  Resolution_2018_lowBremsstrahlung.png  r1  manage  21.2 K  20191021  16:34  AminaZghiche  resolution 
Resolution_2018_lowBremsstrahlung.pdf  r1  manage  37.3 K  20191021  16:33  AminaZghiche  Resolution  
png  Resolution_2018_lowBremsstrahlung_v2.png  r1  manage  20.0 K  20191029  14:34  AminaZghiche  version2 of resolution plots 
Resolution_2018_lowBremsstrahlung_v2.pdf  r1  manage  16.2 K  20191029  14:34  AminaZghiche  version2 of resolution plots  
png  Resolution_2018_inclusive.png  r1  manage  20.0 K  20191021  16:34  AminaZghiche  resolution 
Resolution_2018_inclusive.pdf  r1  manage  36.7 K  20191021  16:33  AminaZghiche  Resolution  
png  Resolution_2018_inclusive_v2.png  r1  manage  19.1 K  20191029  14:34  AminaZghiche  version2 of resolution plots 
Resolution_2018_inclusive_v2.pdf  r1  manage  16.2 K  20191029  14:34  AminaZghiche  version2 of resolution plots  
png  pi0MassEExtal_index_8155.png  r1  manage  26.5 K  20191021  16:08  AminaZghiche  pi0 
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png  pi0MassEBxtal_index_30003.png  r1  manage  28.6 K  20191021  16:08  AminaZghiche  pi0 
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png  mee_in_EE_LowR9_fixedWidthNoFitLine.png  r1  manage  95.8 K  20191021  16:38  AminaZghiche  invariant mass 
mee_in_EE_LowR9_fixedWidthNoFitLine.pdf  r1  manage  22.3 K  20191021  16:38  AminaZghiche  invariant mass  
png  mee_in_EE_HighR9_fixedWidthNoFitLine.png  r1  manage  95.7 K  20191021  16:37  AminaZghiche  invariant mass 
mee_in_EE_HighR9_fixedWidthNoFitLine.pdf  r1  manage  22.0 K  20191021  16:37  AminaZghiche  invariant mass  
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png  mee_in_EB_LowR9_fixedWidthNoFitLine.png  r1  manage  88.7 K  20191021  16:37  AminaZghiche  invariant mass 
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png  mee_in_EB_HighR9_fixedWidthNoFitLine.png  r1  manage  87.7 K  20191021  16:37  AminaZghiche  invariant mass 
mee_in_EB_HighR9_fixedWidthNoFitLine.pdf  r1  manage  21.6 K  20191021  16:37  AminaZghiche  invariant mass  
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png  medianR9eLvstimeinEE.png  r1  manage  57.4 K  20191021  16:36  AminaZghiche  stability 
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png  medianR9eLvstimeinEE_v2.png  r1  manage  52.4 K  20191029  14:26  AminaZghiche  version2 Zee calibration 
medianR9eLvstimeinEE_v2.pdf  r1  manage  48.4 K  20191029  14:26  AminaZghiche  version2 Zee calibration  
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png  medianR9eLvstimeinEB_v2.png  r1  manage  61.5 K  20191029  14:26  AminaZghiche  version2 Zee calibration 
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png  medianmeevstimeinEE_v2.png  r1  manage  78.3 K  20191029  14:26  AminaZghiche  version2 Zee calibration 
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medianmeevstimeinEB.pdf  r1  manage  188.2 K  20191021  16:42  AminaZghiche  intercalibration precision  
png  medianmeevstimeinEB_v2.png  r1  manage  95.6 K  20191029  14:26  AminaZghiche  version2 Zee calibration 
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png  Intercalibration_precision.png  r1  manage  42.4 K  20191021  16:42  AminaZghiche  intercalibration precision 
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Intercalibration_precision_v2.pdf  r1  manage  335.5 K  20191029  14:26  AminaZghiche  version2 Zee calibration  
png  EnergyByRun_Conference.png  r1  manage  77.4 K  20191021  16:09  AminaZghiche  ES plots 
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png  DegradeByLumi_2015Bto2018D4_Rear.png  r1  manage  46.0 K  20191021  16:09  AminaZghiche  ES plots 
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DegradeByLumi_2015Bto2018D4_Front_v2.pdf  r1  manage  18.2 K  20191029  15:34  AminaZghiche  version2 of ES plots 