The value of G F , in turn, is best determined from the muon lifetime where it is often termed . Curiously, a precision measurement of the muon lifetime provided strong bounds on the top quark mass. For many years, the errors on and G F were negligible compared to that of M Z . Indeed, measurements at a muon collider may well improve our knowledge of the Z mass by another order of magnitude. It therefore makes sense to improve the measurement of to the extent that current facilities and technology allow, and to the extent that current theoretical understanding permits us to interpret the result.
Diagrams involving muon loops and virtual hadrons are several orders of magnitude smaller.
Stuart and von Ritbergen also discuss the electroweak corrections to muon decay, which can be separated in a natural way from those involving QED alone. The importance of G F does not end with the top quark mass prediction. Now that the top quark mass has been directly measured and incorporated into the Standard Model, our knowledge of G F will ultimately help in understanding in detail, the Higgs sector, through its radiative corrections. It is the input from G F , through the -parameter, that is responsible for the strongest constraints on sparticle mass splittings in SUSY models. But in the end, we simply do not know what arrangements have been made by nature, and it is our belief that the measurement of fundamental constants, that can be performed with great precision, will be of enduring value.