Top-quark and top-squark production at hadron colliders at electroweak NLO [Elektronische Ressource] / Monika Kollár

Sujets

• Physik

Informations

• Publié par: technische_universitat_munchen
• Publié le: 01 janvier 2007
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Technische Universit¨at Mu¨nchen
Max-Planck-Institut fu¨r Physik
(Werner-Heisenberg-Institut)
Top-Quark and Top-Squark
Production at Hadron Colliders
at Electroweak NLO
Monika Koll´ar
Vollst¨andiger Abdruck der von der Fakult¨at fu¨r Physik
der Technischen Universit¨at Mu¨nchen
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. nat.)
genehmigten Dissertation.
Vorsitzender : Univ.-Prof. Dr. L. Oberauer
Pru¨fer der Dissertation : 1. Univ.-Prof. Dr. W. F. L. Hollik
2. Univ.-Prof. Dr. A. J. Buras
Die Dissertation wurde am 28.03.2007
bei der Technischen Universit¨at Mu¨nchen eingereicht
und durch die Fakult¨at fu¨r Physik am 31.05.2007 angenommen.ToDanoAbstract
In this work, the impact of O(α) contributions on the cross sections for the top-
quark pair production within the SM and for the top-squark pair production within
the MSSM is investigated. For these processes, the EW–QCD interference leads to
2additional contributions atO(αα ) level which are not present at Born-level. In addi-s
tion, parton densities at NLO QED give rise to non-zero photon density in the proton.
It is shown that the size of photon-induced production rates is comparable to other√
EW NLO contributions. The cross sections differential in sˆ and p are studied andT
discussed in kinematic ranges accessible at the LHC and at the Tevatron. The NLO√
EW contributions become significant at high p and high sˆ and should be includedT
in the numerical analysis.
iiiContents
1 Introduction 1
2 Standard Model 5
2.1 Basics of the Standard Model . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Open questions and the role of quantum corrections . . . . . . . . . . . 8
3 Supersymmetry 11
3.1 Motivation for supersymmetry . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Properties of supersymmetric theories . . . . . . . . . . . . . . . . . . . 12
3.2.1 Supersymmetry breaking . . . . . . . . . . . . . . . . . . . . . 13
3.2.2 R-parity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.3 Low-energy supersymmetry . . . . . . . . . . . . . . . . . . . . 15
3.3 The Minimal Supersymmetric Standard Model . . . . . . . . . . . . . . 17
3.4 Particle content of the MSSM . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.1 Quarks and Leptons . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.2 Squarks and Sleptons . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4.3 Higgs and Gauge bosons . . . . . . . . . . . . . . . . . . . . . . 22
3.4.4 Higgsinos and Gauginos . . . . . . . . . . . . . . . . . . . . . . 24
4 Regularization and Renormalization 27
4.1 Regularization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 Renormalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.1 Renormalization schemes . . . . . . . . . . . . . . . . . . . . . . 29
5 Hadronic cross sections 33
5.1 Parton model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 Factorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2.1 Factorization schemes. . . . . . . . . . . . . . . . . . . . . . . . 37
5.2.2 Splitting functions . . . . . . . . . . . . . . . . . . . . . . . . . 38
vvi CONTENTS
5.3 Parton distributions with QED contributions . . . . . . . . . . . . . . . 39
6 Top pair production at NLO QED 41
6.1 Top pair production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.1 tt cross section at the partonic level . . . . . . . . . . . . . . . . 44
6.2 Structure of the NLO QED contributions . . . . . . . . . . . . . . . . . 45
6.2.1 Virtual corrections . . . . . . . . . . . . . . . . . . . . . . . . . 45
6.2.2 Real corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.3 Photon-induced tt production . . . . . . . . . . . . . . . . . . . . . . . 53
6.4 Soft and collinear photon/gluon emission . . . . . . . . . . . . . . . . . 55
6.4.1 Phase space slicing . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.4.2 Dipole subtraction method . . . . . . . . . . . . . . . . . . . . . 58
6.5 Hadronic cross sections for pp/pp→ttX . . . . . . . . . . . . . . . . . 59
6.5.1 Integrated hadronic cross sections . . . . . . . . . . . . . . . . . 60
6.5.2 Differential hadronic cross sections . . . . . . . . . . . . . . . . 60
6.5.3 Mass factorization . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.6 Numerical results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7 SUSY-EW corrections to stop pair production 77
7.1 Top-squark pair production . . . . . . . . . . . . . . . . . . . . . . . . 77
7.1.1 Partonic cross sections at lowest order . . . . . . . . . . . . . . 79
7.2 General aspects of NLO SUSYEW corrections . . . . . . . . . . . . . . 8 0
7.2.1 Quark and squark self-energies at one-loop level . . . . . . . . . 81
7.2.2 On-shell renormalization conditions . . . . . . . . . . . . . . . . 84
7.3 Classification of NLO SUSYEW corrections . . . . . . . . . . . . . . . 85
7.3.1 Virtual corrections . . . . . . . . . . . . . . . . . . . . . . . . . 85
7.3.2 Real corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.4 Photon-induced top-squark production . . . . . . . . . . . . . . . . . . 92
7.5 Numerical results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.6 Analysis of parameter dependence . . . . . . . . . . . . . . . . . . . . . 101
8 Conclusions 107
Zusammenfassung 111
A Choice of parameters 113
A.1 Standard Model Parameters . . . . . . . . . . . . . . . . . . . . . . . . 113
A.2 SPS 1a parameter set of the MSSM . . . . . . . . . . . . . . . . . . . . 114CONTENTS vii
B Basic principles of supersymmetry 117
B.1 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
B.2 Spinors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
B.2.1 Weyl spinors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
B.2.2 Dirac and Majorana spinors . . . . . . . . . . . . . . . . . . . . 119
B.3 Superfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
B.3.1 Grassmann variables . . . . . . . . . . . . . . . . . . . . . . . . 120
B.3.2 Chiral and vector superfields . . . . . . . . . . . . . . . . . . . . 121
B.4 Supersymmetric Lagrangian . . . . . . . . . . . . . . . . . . . . . . . . 122
C Parton densities 125
C.1 LO splitting functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
C.2 QED-modified DGLAP evolution equations. . . . . . . . . . . . . . . . 126
D Loop integrals 127
E Analytical expressions for the NLO QED corrections 131
Bibliography 135
Acknowledgements 153viii CONTENTS