Fermi constant

Fermi constant

[′fer·mē ‚kän·stənt]
(nuclear physics)
A universal constant, introduced in beta-disintegration theory, that expresses the strength of the interaction between the transforming nucleon and the electron-neutrino field.
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Name Symbol Value Fermi constant [G.sub.f] 1.16639 x[10.sup.-5]Ge[V.sup.-2] quark mass t [m.sub.t] 173.5 GeV quark mass b [m.sub.b] 4.65 GeV quark mass [W.sup.+] [m.sub.w] 80.385 GeV Average life of t t 0.5x[10.sup.-24] S Table 2.
Here, [sigma] is the neutron spin; [m.sub.e] is the electron mass, [E.sub.e], [E.sub.v], [p.sub.e], and [p.sub.v] are the energies and momenta of the electron and neutrino, respectively; and [G.sub.F] is Fermi constant of weak interaction (obtained from the [mu]-decay rate).
where [E.sub.e] and [p.sub.e] ([E.sub.v] and [p.sub.v]) are the electron (neutrino) energy and momentum, [m.sub.n] is the neutron mass, [G.sub.F] is the Fermi constant, [V.sub.ud] is the Cabbibo-Kobayashi-Maskawa matrix element, [beta] = [p.sub.e]/[E.sub.e], and F([E.sub.e]) is the Fermi function that describes the interaction of the electron and the recoil proton.