Kaons are mesons (bosonic hadrons). The mesons are all unstable particles of one quark and one anti-quark. They have integral spin and do not obey the Fermi exclusion principle.

Pions that contain only u and d quarks and anti-quarks, and kaons, that contain one u or d quark or anti-quark, and one s quark, are the only mesons that are stable enough leave tracks in a detector.

Note: the table contains only four of the dozens of known mesons. In addition, each meson has an anti-particle.

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