The Weak Interaction

The weak force is one of the four fundamental forces, responsible for the decay of photons into particle antiparticle pairs and the day of neutrons which it does by changing one flavour of quark into another. Each weak interaction involves the exchange of intermediate vector bosons W + , W - and Z 0 . These particles are massive – of the order of 80 GeV, so the range of these forces is very short.

The weak interaction is necessary for nuclear fusion to proceed. This could not happen without the conversion of protons into neutrons, so that deuterium can form take part in the reactions that produce helium, and the production of large numbers of neutrons in explosions of giant stars at the end of their lives makes the production of elements heavier than iron possible.

The discovery of the W and Z particles in 1983 was hailed as a confirmation of the theories which connect the weak force to the electromagnetic forcein electroweak unification.

The weak interaction acts between both quarks and leptons, but the strong force does not act between leptons. Leptons have no color, so they do not participate in the strong interactions, neutrons and neutrinos have no charge, so they experience no electromagnetic forces but all of them join in the weak interaction.

Decay of Neutron

Neutron interacts with neutrino to produce proton and electron

Neutron interacts with neutrino to produce proton and electron. Note the reversal in direction of W is accompanied by change in sign of charge