A Summary of ElectronPhoton Reconstruction Performance in ATLAS

A Summary of Electron/Photon Reconstruction Performance in ATLAS Student Presentation for FAPPS 2008 @ Les Houches Bai Yu Wang Jin Arturo Sanchez

Outline Introduction to Electron/Photon Reconstruction p Energy Measurement p Electron reconstruction p Photon reconstruction p

Introduction Ø Importance – Final state with e orγ( ) Ø What to do – Isolated High Pt Ele/Photon : 1 – QCD background high pt Jet : ~105 Ø How to do – Information from EM calorimeter and ID are used – Electron • High Pt Electrons • Soft Electrons – Photon • Converted • Non Converted （Photon/jet separation） Ø Achievement - Performance

Energy Measurement Ø Effect in Energy Reconstruction – – Upstream Energy Loss Gaps between presampler Lateral leakage out of cluster Longitudinal leakage behind EM calorimeter Ø Energy Reconstruction Formula w 0 : correction for the upstream energy loss w 3 : correction for the energy leakage behind EM calorimeter

Energy Reconstruction : Performance Energy Deviation Energy Resolution

Electron Reconstruction Ø Electron/Jet Separation (High Pt Electron) Ø Electron/Pion Separation (Soft Electron)

Electron/Jet Separation: Performance Cuts R L 1 Trigger and HLT shower shape, Iso 91. 2± 0. 4% （1. 3± 0. 1）× 103 Cut on Track in ID 81. 3± 0. 5% ID-Calo Match 76. 4± 0. 6% （19. 5± 2. 5）× 103 （57± 7）× 103 TRT Cut ~70% ~105 Remove Conversion : Efficiency of Electron R : Rejection factor to the jets ~106

Electron/Pion Separation Ø Important for B-physics (B-tagging) Ø How to Reconstruct soft electron: – Track in ID with Pt>2 Ge. V – Hit by this track in EM calorimeter – Cuts based on shower shape estimator, E/P value, information from TRT

Electron/Pion Separation: Performance Pion Rejection as a function of electron identification efficiency for low energy electron

Photon Reconstruction Ø Converted Photon Reconstruction Ø Non Converted Photon Reconstruction

Converted Photon Reconstruction Ø Conversion is a frequent case for high pt photon(~40% in ) Ø Searched in ID Ø 3(η)× 7(Φ) window in EM calorimeter to reconstruct the Energy Ø Energy reconstruction via dependence of Et, conversion radius and photon energy

Non Converted Photon Reconstruction: Photon/Jet Separation • Photon/Jet Separation – Cuts on EM objects • L 1 Trigger, HLT, shower shapes, isolation – Cuts on EM-ID match • No Track in ± 0. 1×± 0. 1 (η× Φ) around cluster

Photon/jet Separation: Performace Jet rejection as a function of Et of jet for photon identification efficiency remains 80% at low and high luminosity

Conclusion Ø Powerful electron and photon identification algorithm developed – High identification efficiency – Very high QCD background rejection Ø These algorithm and ATLAS detector performance crucial for many discovery channels

Thank you