-- AminaZghiche - 2019-06-19

CMS-DP-2019/0NN

CMS ECAL Performance for Ultra Legacy re-reconstruction of 2017

Abstract: CMS ECAL , calibration and performance in 2017 ultra legacy re-reconstruction.

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iCMS entry


Figure Caption
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pi0MassEBxtal index 30003.png
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pi0MassEExtal index 8155.png
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 = 1.82 (bottom), in the mass range of the π0. Data collected in 2017 and corresponding to an integrated luminosity of approximately 41.5 fb-1 are used. 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 <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 inter-calibrate the energy of ECAL crystals. The π0 mass is obtained before the crystal inter-calibration.
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etaMassEBxtal index 30003.png
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etaMassEExtal index 8155.png
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 Endcapat η = 1.82 (bottom), in the mass range of the η0. Data collected in 2017 and corresponding to an integrated luminosity of approximately 41.5 fb-1 are used. These events are collected by CMS with a dedicated trigger at a rate of 3 (1) 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 η0 candidate. For candidates in the Endcaps, the determination of the photon position in the region with 1.7 <η< 2.55 is improved by the presence of the Preshower, which results in a better mass resolution. The lower trigger rate with respect to π0’s originates from the lower production cross section and branching ratio for decay into two photons (a global factor of about 10). This is partially compensated by the higher selection efficiency due to the larger resonance mass and consequently harder photon energy spectrum, which results in a better energy resolution compared to π0’s. Because of the smaller number of events, the precision of the ECAL inter-calibration with η0’s was lower than the one achieved with π0’s during Run2. However, given the higher energy of the photons, η0’s might provide competitive or better precision than π0’s during Run3 and the HL-LHC.
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medianmeeECALvstimeinEB.png
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medianmeeECALvstimeinEE.png
Time stability of the di-electron invariant mass distribution for the 2017 data taking period using Z→ee electrons. The time stability of the median di-electron invariant mass for the end-of-year (EOY) 2017 calibration (RED) is compared with that of a dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019 (GREEN) for the full 2017 dataset. While for UL a complete re-calibration of the crystals was performed, for EOY only time-dependent effects for the first part of the dataset were accounted for. Both electrons are required to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom). 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" re-samplings. The right panel shows the distribution of the medians.
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medianmeeECALvstimeinEB UL.png
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medianmeeECALvstimeinEE UL.png
Time stability of the di-electron invariant mass distribution for the 2017 data taking period using Z→ee electrons. The plot shows the time stability of the median di-electron invariant mass with a dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019 for the full 2017 dataset. Both electrons are required to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom). 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" re-samplings. The right panel shows the distribution of the medians.
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Error: (1) can't find medianR9eLvstimeinEB.png at /CMSPublic.EcalDPGResultsCMSDPS2019029 pdf version
medianR9eLvstimeinEE.png
Stability of the shower shape of the electromagnetic deposits in the ECAL for leading electrons from Z decays. The plot compares the time stability of the shower shape of the leading electron from Z decays for two calibration sets for the full 2017 dataset: the end-of-year (EOY) 2017 calibration (RED) and a dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019 (GREEN). While for UL a complete re-calibration of the crystals was performed, for EOY only time-dependent effects for the first part of the dataset were accounted for. The event selection requires two electrons to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom). 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" re-samplings. 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, and the offset between the two curves is due to the different treatment of the noise.
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medianR9eLvstimeinEB UL.png
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medianR9eLvstimeinEE UL.png
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 dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019. The event selection requires two electrons to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom). 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" re-samplings. 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, and the offset between the two curves is due to the different treatment of the noise.
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mee in EB.png
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mee in EE.png
Di-electron invariant mass distribution for the 2017 data taking period using Z→ee electrons. The plot shows the di-electron invariant mass distribution for Z decay events with two calibration sets for the full 2017 dataset: the end-of-year (EOY) 2017 calibration (RED) and a dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019 (GREEN). Both electrons are required to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom). The relative resolutions are quoted in the legend, defined as the ratio of σ60 (standard deviation within the smallest interval containing 60% of the data) to μ (mean).
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mee in EB HighR9.png
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mee in EE HighR9.png
Di-electron invariant mass distribution for the 2017 data taking period using Z→ee low-bremsstrahlung electrons. The plot shows the di-electron invariant mass distribution for Z decay events with two calibration sets for the full 2017 dataset: the end-of-year (EOY) 2017 calibration (RED) and a dedicated re-calibration, also called the ultra-legacy calibration (UL), performed in 2019 (GREEN). Both electrons are required to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom) and to have low bremsstrahlung. The relative resolutions are quoted in the legend, defined as the ratio of σ60 (standard deviation within the smallest interval containing 60% of the data) to μ (mean).
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mee in EB LowR9.png
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mee in EE LowR9.png
Di-electron invariant mass distribution for the 2017 data taking period using Z→ee high-bremsstrahlung electrons. The plot shows the di-electron invariant mass distribution for Z decay events with two calibration sets for the full 2017 dataset: the end-of-year (EOY) 2017 calibration (RED) and a dedicated re-calibration, also called the ultra-legacy (UL) calibration, performed in 2019 (GREEN). Both electrons are required to be in the ECAL Barrel (top) or in the ECAL Endcaps (bottom) and to have high bremsstrahlung. The relative resolutions are quoted in the legend, defined as the ratio of σ60 (standard deviation within the smallest interval containing 60% of the data) to μ (mean).
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resolHighR9.png
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resolAll.png
ECAL energy resolution with Zee. Relative electron (ECAL) energy resolution unfolded in bins of pseudo-rapidity η for the ECAL Barrel and the ECAL Endcaps. Electrons from Z→ee decays are used. The resolution is shown separately for very low bremsstrahlung electrons (“golden”, top) and for all electrons (“inclusive”, bottom). The resolution is measured on 2017 data. The relative 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. 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 improves significantly after a dedicated calibration using the full 2017 dataset (UL2017) with respect to the end-of-year-2017 calibration (EOY2017), for which only time dependent effects in the first part of the dataset were corrected for.
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IC precision.png
2017 inter-calibration precision Residual miscalibration of the ECAL channel inter-calibration, as a function of pseudo-rapidity with the dataset recorded during 2017. The red, blue, and green points represent the residual miscalibration of the inter-calibration constants (IC) obtained with three different methods, and the black points represent the residual miscalibrationof 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. The IC combination is performed by weighting the different methods relatively to energy resolution performance as measured in Z→ee decays.
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