Particle Physics any of three short-lived mesons that may be positive, negative, or neutral: pions have a mass c. 270 times that of an electron and play an important role in the binding forces within the nucleus of an atom
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Any of the three least massive mesons, having a positive, neutral, or negative electric charge. The charged pions have a mass 273 times that of an electron and a mean lifetime of 2.6 × 10−8 second, and the neutral pion has a mass 264 times that of an electron and a mean lifetime of 8.4 × 10−17 second. Also called pi meson .