Ferri, Federico (2006) The CMS Electromagnetic Calorimeter for the Higgs boson search H->ZZ^(*)->4e at the LHC. PhD thesis LLR, EP - LLR, EP/X p.199.

Alternative Locations: http://www.imprimerie.polytechnique.fr/Theses/Files/Ferri.pdf

Abstract

The work presented in this thesis has been carried out within the CMS (Compact Muon Solenoid) collaboration. CMS is one of the four experiments that will be installed at the LHC (Large Hadron Collider) at CERN. The thesis if focused on the electromagnetic calorimeter of CMS. The performance of the calorimeter is studied in detail using test beam data as well as a full simulation of the complete detector. The electronic noise in the readout chain is analyzed, and two methods to reconstruct the signal amplitude are proposed, one for signals that saturate the readout electronics while the other is intended to be used in case of noise in the readout chain. The thesis also presents a study of the electron reconstruction in CMS. This study has brought to the first definition of the "quality" measu!
rement of an electron in CMS, to establish a procedure to esta!
blish th
e energy scale measurement of the electrons and to combine the information of calorimetry and tracking to have the best estimate of the electron quadri-momentum at vertex. The results of these studies are applied to the analysis of the Higgs decay channel H->ZZ(*)->4e for which both a standard sequential selection strategy and an optimized neural network technique are proposed.

Table of content

Introduction
1. Standard Model Physics (and Beyond)
1.1 General Concepts
1.1.1 Local Invariance
1.1.2 Spontaneously broken symmetries
1.2 The $SU(2)_L\times U(1)_Y$ Model
1.2.1 The Gauge Sector
1.2.2 Fermions
1.2.3 Anomaly Cancellation
1.2.4 The Higgs Boson
Existing Constraints on $m_H$
1.2.5 }Standard Model Higgs Production in $p-p$ collisions
1.3 Going Beyond
1.3.1 Supersymmetry
1.3.2 Extra-dimensions
Bibliography
2. The CMS Detector at LHC
2.1 The Large Hadron Collider
2.2 The Compact Muon Solenoid
2.2.1 Magnet
2.2.2 Tracker
2.2.3 Electromagnetic Calorimetry
PbWO$_4$ crystals
Mechanical Design
Readout System
Readout Electronics
Energy Resolution
Calibration
Monitoring
2.2.4 Hadron Calorimetry
2.2.5 Muons System
2.2.6 The Trigger and Data Acquisition System
Bibliography
3. ECAL: Test Beam Studies
3.1 Experimental Setup
3.2 Test Beam Results
3.3 Studies on the Amplitude Reconstruction
3.3.1 Noise Monitoring
3.3.2 Amplitude Reconstruction in the Time Domain
3.3.3 Amplitude Reconstruction in Case of Saturated Signals
3.3.4 Amplitude Reconstruction in the Frequency Domain
Pedestal and electron beam run analysis
3.4 Conclusions
Bibliography
4. Electron Reconstruction in CMS
4.1 Electron Propagation towards the Calorimeter
4.2 Electron Candidates
4.2.1 Calorimetric Reconstruction
The Hybrid Algorithm
The Island Algorithm
Optimization for Off-line Reconstruction
Default Energy Scale Correction
4.2.2 Electron \texttt {GSF} Track Reconstruction
4.3 Energy Measurements and Electron Classification
4.4 Energy Scale Correction
4.5 Energy-Momentum Combination
4.6 Effects on the $H\rightarrow ZZ^{(*)}\rightarrow 4e$ physics
4.7 Conclusions
Bibliography
5. The {\relax \mathversion {bold}$H\rightarrow ZZ^{(*)}\rightarrow 4e$} channel
5.1 Signal and Background Definition
5.2 Signal and Background: Generation and Simulation
5.2.1 Signal
5.2.2 Backgrounds
Irreducible background: $ZZ^{(*)}$
Reducible background: $t\overline {t}$
Reducible background: $Zb\overline {b}$
5.3 Events Trigger and Preselection
5.4 Signal Reconstruction and Background Rejection
5.4.1 Off-line reconstruction
5.4.2 Internal Bremsstrahlung
5.4.3 Vertexing
5.4.4 Isolation and Electron Identification
5.4.5 Kinematics of the reconstructed events
5.5 Significance Definition
5.6 Sequential Selection Analysis
5.7 Neural Network Analysis
5.7.1 Neural Network Structure
5.7.2 Multi-Layer Perceptrons
5.7.3 Neural Networks and Probability
5.7.4 Neural Network analysis
5.8 Conclusions
Bibliography
Conclusions
Acknowledgements
Résumé
Riassunto

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