Abstract
The Compact Muon Solenoid (CMS) detector is one of the two multi-purpose experiments at the Large Hadron Collider (LHC) and has a broad physics program. Many aspects of this program depend on our ability to trigger, reconstruct and identify events with final state electrons, positrons, and photons with the CMS detector with excellent efficiency and high resolution. We present the full process of electron and photon reconstruction in CMS, starting from tracker hits and energy deposits in the electromagnetic calorimeter, the methods to achieve the ultimate precision in Run II energy measurements, the identification strategies (based both on cut-based approach and on multivariate analysis) to discriminate prompt electrons and photons from background, and the methods to estimate the associated systematic uncertainties. Finally the performance on benchmark channels (such as Z → e+e−) will be shown.
Highlights
A performant processing of electrons and photons is essential for maximizing the physics potential of the Compact Muon Solenoid (CMS) experiment [1] at the CERN Large Hadron Collider
The Compact Muon Solenoid (CMS) detector is one of the two multi-purpose experiments at the Large Hadron Collider (LHC) and has a broad physics program. Many aspects of this program depend on our ability to trigger, reconstruct and identify events with final state electrons, positrons, and photons with the CMS detector with excellent efficiency and high resolution
We present the full process of electron and photon reconstruction in CMS, starting from tracker hits and energy deposits in the electromagnetic calorimeter, the methods to achieve the ultimate precision in Run II energy measurements, the identification strategies to discriminate prompt electrons and photons from background, and the methods to estimate the associated systematic uncertainties
Summary
A performant processing of electrons and photons is essential for maximizing the physics potential of the CMS experiment [1] at the CERN Large Hadron Collider. This paper gives an overview of electron and photon reconstruction and identification in CMS and discusses the performance on data taken in the last two years. The treatment of electrons and photons with the CMS detector relies primarily on the ECAL with its 75848 quasi-projective scintillating PbWO4 crystals, extending up to a pseudorapidity of |η| = 3.0 with a crack between the barrel and endcaps at |η| = 1.479. The material budget in the endcaps has been reduced by up to 50% This lowers the number of converting photons and bremsstrahlung-emitting electrons, which are challenging for reconstruction algorithms. Important is the steady refinement of the identification algorithms to reduce the number of jets misidentified as prompt electrons or photons, as well as alignments and calibration efforts to keep the residual differences between data and Monte Carlo (MC) simulated events at a minimum
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