Search for the associated production of charginos and neutralinos in proton antiproton collisions at √S=1.96 TeV with the DØ detector at the tevatron [Elektronische Ressource] / vorgelegt von Olav Michael Kåre Mundal. Universität Bonn, Physikalisches Institut

Olav Michael Kare Mundal

Sujets

• Physik

Informations

• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2009
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

..
UNIVERSITAT BONN
Physikalisches Institut
Search for the Associated Production
of Charginos and Neutralinos p
in Proton-Antiproton Collisions at s = 1.96 TeV
with the D Detector at the Tevatron
von
Olav Michael Kare Mundal
Abstract:
A search for Supersymmetry is performed via the associated production of charginos and
neutralinos in nal states consisting of three charged leptons and missing transverse energy
using data collected with the D detector at a center-of-mass energy of 1.96 TeV at the Fermilab
1Tevatron Collider. The data sample corresponds to an integrated luminosity of 2.3 fb . This
nal state is considered one of the most promising channels in the search for supersymmetric
particles because of its low Standard Model background. A dedicated event selection is developed
and events with two muons plus an additional isolated track or events with two electrons plus an
additional isolated track are analyzed. The requirement of an isolated track replaces the third
charged lepton in the event. After all selection cuts are applied, in total 7 events are selected in
the data with an expected number of background events of 5.240.40 (stat)0.30 (syst). Due
to the good agreement of events observed in data with the expectation of the Standard Model
backgrounds, no evidence for Supersymmetry is found. The present analyses are considered in
combination with three other decay channels and limits on the production cross section times
leptonic branching fraction are set. The results are interpreted in a constrained scenario and
exclusion regions are derived as a function of m and m .0 1=2
Post address:
BONN-IR-2009-03
Nu allee 12
Bonn University
D-53115 Bonn
March 2009
Germany. .
UNIVERSITAT BONN
Physikalisches Institut
Search for the Associated Production
of Charginos and Neutralinos p
in Proton-Antiproton Collisions at s = 1.96 TeV
with the D Detector at the Tevatron
Dissertation
zur
Erlangung des Doktorgrades (Dr. rer. nat.)
der
Mathematisch-Naturwissenschaftlichen Fakult at
der
Rheinischen Friedrich-Wilhelms-Universit at Bonn
vorgelegt von
Olav Michael Kare Mundal
aus
Oslo, Norwegen
Bonn 2008Dieser Forschungsbericht wurde als Doktorarbeit von der mathematisch-naturwissenschaftlichen
Fakult at der Universit at Bonn angenommen.
Ersheinungsjarh: 2009
Diese Dissertation ist auf dem Hochschulschriftenserver der ULB Bonn unter http://hss.ulb.uni-
bonn.de/diss online elektronisch publiziert.
Angenommen: Oktober 2008
Referent: Prof. Dr. V. Busc her
Korreferent: Prof. Dr. K. Desch
4Contents
1. Introduction 1
2. Theory 3
2.1. The Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Electroweak Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2. Strong Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3. Higgs Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.4. Problems of the Standard Model . . . . . . . . . . . . . . . . . . . . . . . 10
2.2. Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.1. R-Parity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2.2. Minimal Supersymmetric Standard Model (MSSM) . . . . . . . . . . . . . 13
2.2.3. MSSM Lagrangian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.4. Phenomenological Constraints . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3. Constrained MSSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4. Supersymmetry Breaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5. SUSY Mass Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.6. The Higgs Sector in the MSSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3. Production and Decay of SUSY Particles and Standard Model Background 19
3.1. Production and Decay of P . . . . . . . . . . . . . . . . . . . . . . 19
3.1.1. Production of Charginos and Neutralinos . . . . . . . . . . . . . . . . . . 19
3.1.2. Decay of SUSY Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.3. Signal Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1.4. Analysis Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2. Standard Model Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3. Search for Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3.1. Direct SUSY Searches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3.2. Indirect SUSY Searches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4. Experimental Setup 41
4.1. Coordinate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2. Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3. D Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3.1. Tracking System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3.2. Preshower Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.3.3. The Calorimeter System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.3.4. Muon System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.3.5. The Luminosity Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3.6. Trigger and Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . 54
iContents
5. Phenomenology of pp Collisions 59
5.1. General Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.1.1. Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.1.2. Factorization and Parton Distribution Functions . . . . . . . . . . . . . . 61
5.1.3. K{factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2. Event Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.2.1. Event Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.2.2. Modeling of ISR and FSR . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.2.3. Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2.4. Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6. Physics Objects 67
6.1. Tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.2. Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.2.1. HMatrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.2.2. Electron Likelihood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.3. Muons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.4. Jet Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.4.1. Jet Energy Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.5. Missing Transverse Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.6. Primary Vertex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
7. Data and Monte Carlo Samples 79
7.1. Data Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.1.1. Data Skims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.1.2. Data Quality Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.1.3. Trigger Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.1.4. Integrated Luminosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.2. Monte Carlo Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.2.1. Standard Model Background Monte Carlo Samples . . . . . . . . . . . . . 83
7.2.2. Signal Monte Carlo Generation . . . . . . . . . . . . . . . . . . . . . . . . 84
7.3. Background from QCD Jet Production . . . . . . . . . . . . . . . . . . . . . . . . 88
8. Monte Carlo Corrections and Data Monte Carlo Comparisons 93
8.1. Lepton Reconstruction and Identi cation E ciency Corrections . . . . . . . . . . 93
8.1.1. Muon E ciency Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.1.2. Electron E ciency . . . . . . . . . . . . . . . . . . . . . . . . 95
8.2. E ectiv e Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.3. Electron Energy Resolution and Scale Corrections . . . . . . . . . . . . . . . . . 102
8.4. Muon Smearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
28.5. Track Reweighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
8.6. Z-p Reweighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109T
8.7. Reweighting of the Instantaneous Luminosity Pro le . . . . . . . . . . . . . . . . 110
28.8. Track Smearing, Reconstruction E ciency and =ndof Reweighting. . . . . . . . 110
8.9. Description of the Track Isolation Variable . . . . . . . . . . . . . . . . . . . . . . 111
8.10. Reference Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
8.10