Book/Dissertation / PhD Thesis

PUBDB-2017-07624

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Scrutinizing the Top Quark at Lepton Colliders with Higher Orders

Chokoufe, B. (Corresponding author)DESY* ; Reuter, J. (Thesis advisor)DESY* ; Moch, S.-O. (Thesis advisor)Extern*

2017
Verlag Deutsches Elektronen-Synchrotron Hamburg

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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-07624

Report No.: DESY-THESIS-2017-029

Abstract: In this thesis, we present detailed studies of top-pair production with($t \bar t H$) and without association of a Higgs boson ($t \bar t$) in$e^+e^-$ collisions.These processes are of utmost interest for the top physics programof future lepton colliders.They allow in particular a precise measurement of the top quark mass andthe Yukawa coupling.For this purpose, we present predictions for off-shell $t \bar t$ and$t \bar t H$ production including non-resonant and interferencecontributions up to next-to-leading order (NLO) in perturbative quantum chromodynamics (QCD).This allows for top-quark phenomenology in the continuum at anunprecedented level of accuracy.We show that off-shell effects and NLO QCD corrections forthese processes do not factorize in general.In particular, we present the Yukawa coupling dependence of the crosssection, which receives negative corrections due to sizable interferenceterms.We also add a discussion of $\p_T$ resummation in the form ofcombining the NLO prediction via \textsc{Powheg} matching with the partonshower and the associated uncertainties.To handle large Coulomb singularities at threshold, we include thenext-to-leading log (NLL) threshold resummation derived in nonrelativistic QCD (NRQCD) for $t \bar t$ production.This results in a form factor that we incorporate in a fullyrelativistic cross section, which is factorized within an extendeddouble-pole approximation.Fixed-order QCD corrections are included, hereby, for the top decay.We combine this calculation with the full fixed-order QCD results at NLO for $W^+b W^-\bar b$ production to obtain a computation that is not onlyvalid at threshold but smoothly interpolates to the continuum.This allows us to present the first prediction for exclusive $W^+b W^-\bar b$production at a lepton collider with a consistent matching between thetop-antitop threshold and continuum regions.This computation is not only required to describe the intermediateenergy region but also allows to study threshold resummation effects infully differential distributions and incorporates important electroweakand relativistic corrections.All computations are implemented within the automated NLO MonteCarlo event generator \textsc{Whizard}.Thus, we review the important aspects of the program and variousnew features that we have implemented.

Note: Dissertation, Universität Hamburg, 2017

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Contributing Institute(s):

1. Theorie-Gruppe (T)

Research Program(s):

1. 611 - Fundamental Particles and Forces (POF3-611) (POF3-611)
2. PHGS, VH-GS-500 - PIER Helmholtz Graduate School (2015_IFV-VH-GS-500) (2015_IFV-VH-GS-500)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2017

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Database coverage:

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