7.3 Weak Force

This manifests itself through nuclear β decay,

n p + e + ν e ¯ . (7.7)

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± 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± bosons are charged, and the Z 0 boson is neutral. The typical β decay referred to above is mediated by a W boson as can be seen in the Feynman diagram figure 7.1 . 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 7.1: The Feynman diagram for the weak decay of a neutron.