W-pair production near threshold in unstable particle effective theory [Elektronische Ressource] / vorgelegt von Pietro Falgari

W-pair production near threshold inunstable-particle effective theoryVon der Fakult¨at fu¨r Mathematik, Informatik undNaturwissenschaften der RWTH Aachen University zurErlangung des akademischen Grades eines Doktors derNaturwissenschaften genehmigte Dissertationvorgelegt vonDottore Magistrale in FisicaPietro Falgariaus Bergamo, ItalienBerichter: Universit¨atsprofessor Martin BenekeUniversit¨atsprofessor Werner BernreutherTag der mu¨ndlichen Pru¨fung: 7. November 2008Diese Dissertation ist auf den Internetseiten der Hochschulbibliothekonline verfu¨gbar.Abstract− +Inthisthesiswepresentadedicated studyofthefour-fermionproductionprocesse e →− ¯ ν¯ udX near the W-pair production threshold, in view of its importance for a precisedeterminationoftheW-bosonmassattheILC.Thecalculation isperformedintheframe-work of unstable-particle effective theory, which allows for a gauge-invariant inclusion ofinstability effects, and for a systematic approximation of the full cross section with anexpansion in the coupling constants, the ratio Γ /M , and the non-relativistic velocityW Wv of the W boson. The effective-theory result, computed to next-to-leading order in the2expansion parameters Γ /M ∼ α ∼ v , is compared to the full numerical next-to-W W ewleading order calculation of the four-fermion production cross section, and agreement tobetter than 0.5% is found in the region of validity of the effective theory.