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Radiating top quarks
Gosselink, M.
Publication date 2010
Link to publication
Citation for published version (APA):
Gosselink, M. (2010). Radiating top quarks.
http://www.nikhef.nl/pub/services/biblio/theses_pdf/thesis_M_Gosselink.pdf
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Contents
Introduction 1
1 Top quark physics 5
1.1 Physics at the LHC . . . 5
1.2 Understanding the top quark . . . 9
1.2.1 Mass . . . 9
1.2.2 Decay . . . 10
1.2.3 Pair production . . . 11
1.2.4 Single top production . . . 18
1.3 Top quarks at the LHC . . . 19
1.3.1 Parton distribution functions . . . 19
1.3.2 Top quark mass and the Higgs boson . . . 21
1.3.3 Non-Standard Model top decays and t¯t resonances . . . 22
1.3.4 Pair production with additional jets . . . 23
2 Monte Carlo generators 25 2.1 Generator overview . . . 25
2.1.1 Hard scattering . . . 27
2.1.2 Parton showers . . . 28
2.1.3 Hadronisation and decay . . . 32
2.1.4 Underlying event . . . 33
2.2 Combining partons showers with matrix elements . . . 35
2.2.1 Matrix element correction for the parton shower . . . 35
2.2.2 Matching the parton shower with NLO matrix elements . . . 36
2.2.3 Merging the parton shower with tree-level matrix elements . . . . 38
2.2.4 Comparisons . . . 44
2.3 Conclusions . . . 47
Contents
3 Detection of top quarks in ATLAS 49
3.1 The ATLAS detector . . . 50
3.1.1 Inner detector . . . 50
3.1.2 Calorimeters . . . 53
3.1.3 Muon spectrometer . . . 58
3.1.4 Trigger system . . . 60
3.2 Jet reconstruction . . . 61
3.2.1 Input to jet reconstruction . . . 61
3.2.2 Jet clustering algorithms . . . 63
3.2.3 Jet calibration . . . 66
3.2.4 Jet reconstruction performance . . . 68
3.3 The typical t¯t event . . . 70
4 Production of W + jets, t¯t, and t¯tH 73 4.1 Momentum fractions . . . 73
4.2 Reconstruction of x1 and x2 . . . 75
4.2.1 Neutrino momentum . . . 75
4.2.2 Jets and acceptance . . . 75
4.2.3 Jet multiplicity . . . 78
4.2.4 Hadronic W± boson events . . . . 79
4.3 Conclusions . . . 80
5 Cross section at √s = 14 TeV 81 5.1 Event topology . . . 82 5.2 Object definitions . . . 84 5.3 Event selection . . . 85 5.3.1 Trigger . . . 85 5.3.2 Preselection . . . 85 5.3.3 Selection efficiencies . . . 86 5.4 Top reconstruction . . . 87
5.4.1 Hadronic top quark mass . . . 87
5.5 Cross section determination . . . 91
5.6 Statistical and systematic uncertainties . . . 92
5.6.1 Luminosity . . . 92
5.6.2 Parton density functions . . . 93
5.6.3 Lepton identification and trigger efficiencies . . . 94
5.6.4 Initial and final state radiation . . . 94
5.6.5 Fit uncertainties . . . 95
5.6.6 Jet energy scale . . . 95
5.6.7 Amount of background . . . 97
5.7 Results and conclusions . . . 97
Contents
6 Top quark pairs with additional jets 99
6.1 Event selection . . . 99
6.1.1 QCD multi-jet background . . . 99
6.1.2 Including b-tagging . . . 101
6.2 Jet multiplicity . . . 104
6.2.1 Jet spectrum . . . 105
6.2.2 Fast versus full simulation . . . 107
6.2.3 Event generator comparison . . . 108
6.3 t¯t cross section measurement . . . 109
6.3.1 Event selection . . . 109
6.3.2 Mass reconstruction . . . 109
6.4 Conclusions and discussion . . . 112
7 W± and Z boson production 115 7.1 Comparison . . . 115
7.2 Cross sections . . . 116
7.3 W± and Z boson spectra . . . 118
7.4 Jet spectra . . . 120
7.5 Ratio of W + jets and Z + jets events . . . 123
7.6 Underlying event . . . 125
7.7 Background from W + jets in t¯t event selection . . . 128
7.8 Conclusions & Discussion . . . 131
8 Outlook 133 A List of MC generators and samples 137 A.1 Monte Carlo generators . . . 137
A.2 Samples for √s = 14 TeV . . . 137
A.3 Samples for √s = 10 TeV . . . 140
B Generator comparison 141 B.1 MC@NLO, Alpgen, and AcerMC . . . 141
B.2 AcerMC/Pythia: ISR and FSR variation . . . 143
References 145
Summary 157
Samenvatting 159
Acknowledgements 161
