In particle physics
, strangeness S
is an additive quantum number
that is conserved in all interactions not involving the weak force
The concept originated out of necessity in the early 1950s, when experiments showed "V particles" (now known as kaons) were produced with cross sections indicative of the strong force, but decayed on the slower time scale of the weak force. The new quantum number was named by Murray Gell-Mann, the Joyce-reading theorist more famously known for dubbing the constituent particles of hadrons "quarks."
Conservation of S under the conditions mentioned means that strange particles, kaons and hyperons, must be produced in pairs, so that the opposite signs of their strangeness cancel and leave a net S of zero. Note that this production need not necessarily be of strange particle and antiparticle; a kaon can be produced along with a hyperon provided the necessary additional particles show up to fulfill all the other relevant conservation laws.
A positive (positive in this sense refers to electric charge) kaon (K+) is defined to have a strangeness of 1, and its antiparticle K-, found to be produced along with the positive kaon, thus has strangeness -1. The neutral kaon and antikaon likewise have opposite strangeness, and the strangeness of all the hyperons can be worked out from observed reactions as well.
In the quark model, the strange quark s has a strangeness of -1, with its antiquark having strangeness +1. No other quarks have nonzero values of this quantum number.