Strangeness was introduced by
Murray Gell-Mann,
Abraham Pais,
Tadao Nakano and
Kazuhiko Nishijima to explain the fact that certain particles, such as the
kaons or the
hyperons and , were created easily in particle collisions, yet decayed much more slowly than expected for their large masses and large production
cross sections. Noting that collisions seemed to always produce pairs of these particles, it was postulated that a new conserved quantity, dubbed "strangeness", was preserved during their creation, but
not conserved in their decay. In our modern understanding, strangeness is conserved during the
strong and the
electromagnetic interactions, but not during the
weak interactions. Consequently, the lightest particles containing a strange quark cannot decay by the strong interaction, and must instead decay via the much slower weak interaction. In most cases these decays change the value of the strangeness by one unit. This doesn't necessarily hold in second-order weak reactions, however, where there are mixes of and mesons. All in all, the amount of strangeness can change in a weak interaction reaction by +1, 0 or −1 (depending on the reaction). For example, the interaction of a K− meson with a proton is represented as: K^-+p \rightarrow \Xi^0+K^0 (-1) + (0) \rightarrow (-2) + (1) Here strangeness is conserved and the interaction proceeds via the strong nuclear force. Nonetheless, in reactions like the decay of the positive kaon: K^+ \rightarrow \pi^+ + \pi^0 +1 \rightarrow (0) + (0) Since both pions have a strangeness of 0, this violates conservation of strangeness, meaning the reaction must go via the weak force. ==See also==