pi-meson

(′pī ′mā′sän)

(particle physics) Collective name for three semistable mesons which have charges of +1, 0, and -1 times the proton charge, and form a charge multiplet, with an approximate mass of 138 megaelectronvolts, spin 0, negative parity, negative G parity, and positive charge parity (for the neutral meson). Also known as pion. Symbolized π. Any meson belonging to an isospin triplet with hypercharge 0, negative G parity, and positive charge parity (for the neutral meson).

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IN BRIEF: n. - A fundamental particle made up of a quark and an antiquark involved in holding the nucleus together.