Electron and Photon Identification Performance in ATLAS

TL;DR

This paper discusses the methods and performance of electron and photon identification in the ATLAS detector, including calibration, reconstruction, and analysis techniques to distinguish these particles from background at the LHC.

Contribution

It presents the calibration procedures, identification algorithms, and performance metrics for electrons and photons in ATLAS, highlighting improvements in particle discrimination.

Findings

Achieved electron rejection factor of 10^5 against QCD jets.

Developed calibration techniques using Z -> ee events.

Compared cut-based and multivariate identification methods.

Abstract

The understanding of the reconstruction and calibration of electrons and photons is one of the key steps at the start-up of data-taking with ATLAS at the LHC (Large Hadron Collider). The calorimeter cells are electronically calibrated before being clustered. Corrections to local position and energy measurements are applied to take into account the calorimeter geometry. Finally, longitudinal weights are applied to correct for energy loss upstream of the calorimeter. As a last step the Z -> ee events will be used for in-situ calibration using the Z boson mass. The electron identification is based on the shower shape in the calorimeter and relies heavily on the tracker and combined tracker/calorimeter information to achieve the required rejection of 10^5 against QCD jets for a reasonably clean inclusive electron spectrum above 20-25 GeV. For photon identification, in addition to the shower shape in the calorimeter, recovery of photon conversions is an essential ingredient given the large amount of material in the inner tracker. The electron and photon identification methods (cuts and multivariate analysis) will be discussed.