The determination of the Fermi coupling constant, G F , is examined in the light of recently calculated 2-loop QED corrections and planned experiments to measure the muon lifetime to a level below 1 ppm. The methods used in the calculation of the QED corrections are described in detail. Sources of the dominant theoretical and experimental uncertainties are identified. Finally the incorporation of G F into analyses using the full electroweak Standard Model is discussed.
Hadronic corrections to the muon lifetime are calculated in the Fermi theory in the presence of QED using dispersion relations. The result, after convolution of hadron data with the calculated perturbative kernel is ∆Γ had = −Γ 0 α π 2 2 0.00058.
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