The Need For Strangeness
In 1947 the British physicists Rochester and Butler observed new particles. These particles came in two forms: a neutral one that decayed into the pions π+ and π- , and a positively charged one that decayed into a muon (heavy anti-electron) and a photon. Later a negative one was observed.
The life time of these particle was much longer than would be expected if they decayed via the strong force - 10-10 s as opposed to 10-15 s . The decay time is what would be expected if the particles decayed via the weak interaction. When a K+, the lightest particle to contain a strange quark, decays to a π+, nade up of ordinary quarks, a strange quark is converted into a “down” quark.Using accelerators it was found that strange particles are formed in pairs, suggesting a strangeness conservation law. Strange particles, but because decay of strange particles appears to occur via the weak interation, it is believed that the weak interaction does not conserve strangeness.