W-pair production near threshold in unstable particle effective theory

In this thesis we present a dedicated study of the four-fermion production process e- e+ ---> mu- nubar_mu u dbar X near the W-pair production threshold, in view of its importance for a precise determination of the W-boson mass at the ILC. The calculation is performed in the framework of unstable-particle effective theory, which allows for a gauge-invariant inclusion of instability effects, and for a systematic approximation of the full cross section with an expansion in the coupling constants, the ratio Gamma_W/M_W, and the non relativistic velocity v of the W boson. The effective-theory result, computed to next-to-leading order in the expansion parameters Gamma_W/M_W ~ alpha_ew ~ v^2, is compared to the full numerical next-to-leading order calculation of the four-fermion production cross section, and agreement to better than 0.5 % is found in the region of validity of the effective theory. Furthermore, we estimate the contributions of missing higher-order corrections to the four-fermion process, and how they translate into an error on the W-boson mass determination. We find that the dominant theoretical uncertainty on M_W is currently due to an incomplete treatment of initial-state radiation, while the remaining combined uncertainty of the two NLO calculations translates into dM_W ~ 5 MeV. The latter error is removed by an explicit computation of the dominant missing terms, which originate from the expansion in v of next-to-next-to leading order Standard Model diagrams. The effect of resummation of logarithmically enhanced terms is also investigated, but found to be negligible.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2008

Author dc:creator

• Falgari, Pietro

Contributors dc:contributor

• Beneke, Martin

• info:eu-repo/classification/ddc/530
• Elementarteilchenphysik
• Physik
• particle physics phaenomenology
• effective theories
• unstable particles
• W bosons

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113124%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50584