Fermi's Interaction - Fermi Constant

Fermi Constant

The strength of Fermi's interaction is given by the Fermi coupling constant G_F. The most precise experimental determination of the Fermi constant comes from measurements of the muon lifetime, which is inversely proportional to the square of G_F. In modern terms:

$\frac{G_\text{F}}{(\hbar c)^3}=\frac{\sqrt{2}}{8}\frac{g^{2}}{m_\text{W}^{2}}=1.16637(1)\times10^{-5} \; \textrm{GeV}^{-2} \ .$

Here g is the coupling constant of the weak interaction, and m_W is the mass of the W boson which mediates the decay in question.

In the Standard Model, Fermi's constant is related to the Higgs vacuum expectation value

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