The strange quark is the third lightest quark of the Standard Model. It was introduced in response to the strange behaviour of certain particles that arise from a strong interaction but can only decay via weak interactions. The number of strange quarks in a hadron is called “strangeness”. Bound states of quarks that interact via strong or electromagnetic force conserve this quantum number, while weak decays do not, as they transform the strange quark into a different flavour.
Together with the up and down quarks, the strange quark can be used to classify bound states based on their quark content. M. Gell-Mann and Y. Ne’eman independently postulated the so-called “Eightfold Way”, which systematically arranges the eight lightest mesons and can be also applied to baryons. The particles are sorted, among other parameters, according to their strangeness.
The lightest mesons featuring a strange quark, bound to either an up or a down quark, are called kaons (K).
The strange quark was first experimentally detected, together with the up and down quarks, at SLAC in California in 1969.
The meson octet is a graphical representation of the eight lightest mesons, composed by u, d and s-quarks, based on the concept of “Eightfold Way”. These are organised, among other parameters, according to their strangeness number.
