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Precise predictions for W-pair production at a future linear collider

English title Precise predictions for W-pair production at a future linear collider
Applicant Denner Ansgar
Number 109164
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Theoretical Physics
Start/End 01.11.2005 - 31.10.2006
Approved amount 47'460.00
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Keywords (11)

particle phenomenology; elektroweak interaction; w-pair production; higher-order corrections; physics at linear e+e- colliders; elementary particle physics; weak interaction; electroweak standard model; precision tests; electroweak radiative corrections; 4-fermion production

Lay Summary (English)

Lay summary
Future electron--positron colliders will enable improved precision tests of the Standard Model of the electroweak interaction. These include W-pair production which will allow for an accurate measurement of the W-boson mass and triple gauge-boson couplings. While the cross section far above threshold will be measured with an accuracy at the few per-mille level, a scan of the threshold region will provide a measurement of the W-boson mass with an accuracy of 6 MeV. These goals require theoretical predictions with sufficiently high precision.The aim of the project is to calculate the cross section for W-pair production with an accuracy of a few per mille. To this end, the complete one-loop electroweak radiative corrections to 4-fermion production, e+e- -> 4f, have to be calculated, and the leading higher-order corrections have to be taken into account.The calculation of the electroweak corrections to e+ e- -> 4f is a technical challenge. For the simplest final state, about 2000 Feynman diagrams contribute, for the most complicated final state, there are more than 20000 diagrams. While the algebraic reduction of these diagrams to simple building blocks can in principle be done with existing computer algebra codes, the large number and complexity of the diagrams requires to develop improved reduction algorithms. This and the calculation of the diagrams is one core part of the project.The numerical evaluation of the complicated loop integrals in the standard approach is plagued by severe numerical problems, which make a calculation of the electroweak corrections to e+ e- -> 4f in the standard approach impossible. Therefore, we have to develop and to implement improved techniques for the calculation of one-loop integrals. This forms a second core part of the project.A conceptual problem in the calculation of radiative corrections to processes involving unstable gauge bosons is the introduction of the gauge-boson decay width. To this end, we use a generalization of the complex-mass scheme. This scheme respects the full SU(2) x U(1) gauge invariance.So far, we have implemented the virtual corrections for the simplest final states into the Monte Carlo generator RacoonWW and produced numerical results for physical distributions. However, before we have a satisfactory generator many improvements are necessary. We have to speed up the numerical calculation and to eliminate any remaining numerical instabilities. We have to implement the leading higher-order corrections and to estimate the remaining theoretical uncertainty. Finally, we would like to extend our calculation to the remaining, more complicated, four-fermion final states.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


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Associated projects

Number Title Start Funding scheme
66712 Precise predictions for W-pair production at a future linear collider 01.11.2002 Project funding (Div. I-III)