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出典:『Wikipedia』 (2011/07/07 09:58 UTC 版)

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In particle physics, mesons (pronounced /ˈmiːzɒnz, ˈmɛzɒnz/) are subatomic particles composed of one quark and one antiquark. All mesons are unstable, with the longest-lived lasting for only a few 100-millionths (10⁻⁸) of a second. Mesons have a physical size, with a radius a little smaller than the size of a proton or neutron (i.e. one femtometer: 10⁻¹⁵ m). Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons. Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of cosmic ray interaction with matter—a typical high-energy interaction between particles made of quarks (in cosmic ray interactions, these are ordinary protons and neutrons). Mesons are also frequently produced in high-energy particle accelerators that collide protons, anti-protons, or other particles containing quarks.