Photon triggers in ATLAS

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Table of contents

1 Introduction 
1.1 The Standard Model of particle physics
1.1.1 Gauge invariance in Quantum Electrodynamics
1.1.2 Electroweak theory
1.1.3 Introduction to QCD
1.1.4 The Higgs mechanism
1.1.5 Theoretical constraints on the Higgs mass
1.2 Review of Higgs searches
1.2.1 Direct searches
1.2.2 Indirect constraints
1.3 Review of di-photon cross-section measurements
1.4 Motivation and structure for this thesis
2 Accelerator and detector 
2.1 Introduction to LHC
2.2 The ATLAS Detector
2.2.1 Coordinate system and nomenclature
2.2.2 Physics requirement and performance goals
2.2.3 Overview of the ATLAS detector
2.2.4 Magnet system
2.2.5 Inner detector
2.2.6 Calorimeter
2.2.7 Muon spectrometer
2.2.8 Trigger and data acquisition system
2.3 ATLAS data taking status and performance
2.3.1 Performance of the Inner Detector
2.3.2 Performance of the calorimeter
2.3.3 Performance of the muon spectrometer
2.3.4 Trigger and event selection
2.3.5 Material mapping in the ID
3 Photon reconstruction, calibration and identication 
3.1 Photon reconstruction
3.2 Photon calibration
3.3 Photon identification
4 Photon Trigger Eciency 
4.1 Introduction
4.2 Photon triggers in ATLAS
4.3 Triggers items and the corresponding selection criteria
4.4 Photon trigger efficiency measurement: description of the methods
4.4.1 The tag & probe method
4.4.2 The bootstrap method
4.4.3 The electron-to-photon extrapolation method
4.5 Monte Carlo study
4.5.1 Reconstructed photon selection criteria
4.5.2 Monte Carlo samples
4.5.3 Results of the tag&probe method
4.5.4 Tag&probe systematics
4.5.5 Results of bootstrap method
4.5.6 Bootstrap systematics
4.5.7 Comparison between the tag&probe and bootstrap samples
4.5.8 The electron to photon extrapolation method
4.5.9 Electron extrapolation systematics
4.5.10 Comparison of the three data-driven methods
4.5.11 Conclusion
4.6 Efficiency measurement on real data
4.6.1 g20 loose efficiency measurement
4.6.2 g10 loose efficiency for inclusive photon cross-section measurement .
5 Isolated di-photon cross-section measurement 
5.1 Di-photon production and background processes
5.1.1 signal processes
5.1.2 Background process
5.2 Data and Monte Carlo samples
5.3 Photon and event selection
5.3.1 Photon isolation
5.3.2 Other photon identification criteria
5.3.3 Event selection
5.4 Extraction of the di-photon signal
5.4.1 Extraction of the yields
5.4.2 Signal isolation transverse energy one-dimensional PDF
5.4.3 Background isolation transverse energy one-dimensional PDF
5.4.4 Two-dimensional jj isolation transverse energy PDF
5.4.5 Tests on Monte Carlo
5.4.6 Results on real data
5.4.7 Systematic uncertainties
5.4.8 Differential spectra
5.5 Other methods
5.5.1 2×2D sideband
5.5.2 4×4 matrix
5.5.3 Comparison of the three methods
5.6 Differential cross-section
5.6.1 Extract the background from electrons
5.6.2 Trigger efficiency
5.6.3 Identification efficiency
5.6.4 Unfolding matrix
5.6.5 Reconstruction efficiency
5.6.6 Final result
6 H → γγ analysis 
6.1 Signal and background processes
6.1.1 Higgs production
6.1.2 Higgs decay
6.1.3 Background processes
6.2 Discriminating variables
6.3 Principles of an early H → γγ analysis
6.3.1 Photon selection
6.3.2 Event selection
6.3.3 Primary vertex reconstruction
6.3.4 Extraction of the exclusion limit
6.4 Assessment of the exclusion limit from Monte Carlo simulation
6.4.1 Event-level trigger efficiency measurement
6.4.2 Signal and background estimation
6.4.3 Extrapolation to 7 TeV
6.4.4 Incorporating systematics uncertainties
6.5 Sensitivity on 2010 data
6.5.1 Trigger efficiency measurement
6.5.2 Analysis on real data: background decomposition using the di-photon analysis technique
6.5.3 Comparison with the Monte Carlo prediction
6.5.4 Projected sensitivity
6.6 Conclusion and prospects