Fermi's Interaction - Fermi Constant

Fermi Constant

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