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| Book/Dissertation / PhD Thesis | PUBDB-2017-07541 |
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2017
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-07541
Report No.: DESY-THESIS-2017-025
Abstract: Experiments in high energy physics have reached an unprecedented accuracy. Thisaccuracy has to be matched by the theoretical predictions used to search for new physics.For this purpose, sophisticated computer programs are necessary, both for the calculationof matrix elements (tree-level and loop) and in the field of Monte-Carlo event generation.The hadronic initial state at the LHC poses signifcant challenges for measurement andsimulation. A future lepton collider, like the proposed international linear collider (ILC)in Japan or compact linear collider (CLIC) at CERN would have a much cleaner initialstate. Such a machine would achieve an even higher precision. In the field of leptoncolliders, the Whizard event generator has been established as the program of choicedue to its unique treatment of beam structure functions and initial-state radiation. Inthis thesis, we present the extension of Whizard to next-to-leading order accuracy,thus augmenting it to the state of the art. We use the Frixione-Kunszt-Signer (FKS)subtraction scheme to subtract divergences, of which a detailed outline is given. Thisnew functionality is used to perform in-depth studies of the top quark. Being the heaviestparticle in the standard model, its strong connection to the Higgs sector as well as itsabundant production at a future lepton collider makes it an excellent object of study.Yet, its lifetime is very short and high-multiplicity final-states of its decay products aredecayed in the detector.This thesis investigates the influence of NLO QCD corrections to the fully off-shell topproduction processes e + e − → μ + ν μ e − ν ̄ e b ̄ b and e + e − → μ + ν μ e − ν ̄ e b ̄ bH. These calcuationshave not been performed for the first time. Moreover, the incorporation of NLO QCDcorrections into the resummation of the top production threshold and its matching tothe relativistic continuum for the process e + e − → bW + ̄ bW − . All results are obtainedwith Whizard interfaced to the matrix-element generator OpenLoops.
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