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6.4: Weak Nuclear Force

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  • The weak nuclear force manifests itself through nuclear \(\beta\) decay, \[n\rightarrow p+e^{-}+\overline{\nu}_e.\] The standard coupling for this theory is called the Fermi coupling, \(G_F\), after its discoverer. After the theory was introduced it was discovered that there were physical particles that mediate the weak force, the \(W^{\pm}\) and the \(Z^0\) bosons. These are very heavy particles (their mass is about 80 times the proton mass!), which is why they have such a small range – fluctuations where I need to create that much mass are rare. The \(W^{\pm}\) bosons are charged, and the \(Z^0\) boson is neutral. The typical \(\beta\) decay referred to above is mediated by a \(W^-\) boson as can be seen in the Feynman diagram in Figure \(\PageIndex{1}\). The reason for this choice is that it conserves charge at each point (the charge of a proton and a \(W^-\) is zero, the charge of an electron and a neutrino is -1, the same as that of a \(W^-\)).

    Figure \(\PageIndex{1}\): The Feynman diagram for the weak decay of a neutron.