Abstract
Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high resolution electron and photon energy measurements. Excellent energy resolution is crucial for studies of Higgs boson decays with electromagnetic particles in the final state, as well as searches for very high mass resonances decaying to energetic photons or electrons. The CMS electromagnetic calorimeter (ECAL) is a fundamental instrument for these analyses and its energy resolution is crucial for the Higgs boson mass measurement. Recently the energy response of the calorimeter has been precisely calibrated exploiting the full Run2 data, aiming at a legacy reprocessing of the data. A dedicated calibration of each detector channel has been performed with physics events exploiting electrons from W and Z boson decays, photons from π0 and η decays, and from the azimuthally symmetric energy distribution of minimum bias events. This talk presents the calibration strategies that have been implemented and the excellent performance achieved by the CMS ECAL with the ultimate calibration of Run2 data, in terms of energy scale stability and energy resolution.
Highlights
The Compact Muon Solenoid (CMS) experiment [1] at the CERN Large Hadron Collider is equipped with a scintillating crystal electromagnetic calorimeter (ECAL) [2], made of 75848 lead tungstate scintillating crystals
This paper presents the ECAL calibration methods used for the Run2 “ultra-legacy” reprocessing and results, with a particular emphasis on the computing aspects
The ECALELF framework provides the ability to reprocess the W and Z electrons recorded in one year in two hours on the CERN batch system, it is a powerful tool to check the effects of new laser corrections or calibration constants
Summary
The Compact Muon Solenoid (CMS) experiment [1] at the CERN Large Hadron Collider is equipped with a scintillating crystal electromagnetic calorimeter (ECAL) [2], made of 75848 lead tungstate scintillating crystals. The CMS experiment has used these calibration sets for the full Run data reprocessing, which has been carried out during Long shutdown 2. This reprocessing constitutes the “ultra-legacy” data set, which will be used for analyses requiring optimal energy resolution and will be preserved for future analyses on Run data. This paper presents the ECAL calibration methods used for the Run2 “ultra-legacy” reprocessing and results, with a particular emphasis on the computing aspects. Many low-level parameters are used to compute the crystal energy deposits and the time of arrival (pedestals, pulse shapes, alignment and synchronization) These parameters are not described in this paper, all of them have been recomputed or checked for the purpose of the “ultra-legacy” reprocessing. In addition Monte Carlo simulation conditions have been derived from data, for each year of Run, in order to achieve an improved description of the detector response and noise
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