CMS DP-2020/021

CMS ECAL Performance for Ultra Legacy re-reconstruction of Run2

Stability of the shower shape of the electromagnetic deposit in the ECAL for the leading electron from Z decays.

The plot shows the time stability of the shower shape of the leading electron in Z decays with a refined re-calibration performed in 2019 for the full Run2 dataset. The event selection requires two electrons to be in the ECAL Barrel or in the ECAL Endcaps. 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.

Invariant mass distribution for electron pairs from Z boson decays.

The plot shows the invariant mass distribution comparing 2016, 2017, and 2018 data-taking period using Z→ee events with a refined re-calibration performed in 2019 for the full Run2 dataset. The event selection requires two electrons to be in the ECAL Barrel or in the ECAL Endcaps. For candidates in the Endcaps, the electron pseudorapidity is required to be lower than 2.5.

Invariant mass distribution for electron pairs from Z boson decays using low-bremsstrahlung electrons.

The plot shows the invariant mass distribution comparing 2016, 2017, and 2018 data-taking period using Z→ee events with a refined re-calibration performed in 2019 for the full Run2 dataset. The event selection requires two electrons to be in the ECAL Barrel or in the ECAL Endcaps. For candidates in the Endcaps, the electron pseudorapidity is required to be lower than 2.5.

Invariant mass distribution for electron pairs from Z boson decays using high-bremsstrahlung electrons.

The plot shows the invariant mass distribution comparing 2016, 2017, and 2018 data-taking period using Z→ee events with a refined re-calibration performed in 2019 for the full Run2 dataset. The event selection requires two electrons to be in the ECAL Barrel or in the ECAL Endcaps. For candidates in the Endcaps, the electron pseudorapidity is required to be lower than 2.5.

Residual mis-calibration of the ECAL channel inter-calibration, as a function of pseudorapidity with the dataset recorded during LHC Run 2.

The calibration is obtained by combining three methods: electrons from Z→ee decays using the known Z boson mass as energy reference, electrons from W and Z boson decays using the tracker momentum as energy reference, and photons from π0→γγ decays are used by the calibration methods. The combination is performed by weighting the different methods relatively to their energy resolution performance as measured in Z→ee decays. For |η|>2.5, only Z→ee decays are used. The dashed-line represents the end of the Ecal Barrel (|η| < 1.49), while the full line refers to the end of the tracker acceptance (|η| < 2.5). For the very forward electrons (|η| >2.5), the degradation of the precision is explained by the usage of a single calibration method, the lower intrinsic ECAL performance, and the degraded triggering capability due to the absence of tracker. This shows a good stability overtime of the calibration precision despite the increase of the LHC luminosity and the ageing of the detector.