[an-tee-pahr-ti-kuh
l, an-tahy-] 
| a particle all of whose properties, as mass, spin, or charge, have the same magnitude as but, where appropriate, the opposite sign of a specific elementary particle; neutral pions, photons, and gravitons are considered to be their own antiparticles: The positron is the antiparticle of the electron. Compare antimatter, annihilation (def. 3). |
| an·ti·par·ti·cle (ān'tē-pär'tĭ-kəl, ān'tī-) n. A subatomic particle, such as a positron, antiproton, or antineutron, having the same mass, average lifetime, spin, magnitude of magnetic moment, and magnitude of electric charge as the particle to which it corresponds but having the opposite sign of electric charge, opposite intrinsic parity, and opposite direction of magnetic moment. See Table at subatomic particle. |
In physics, a rare form of subatomic matter that is a mirror image of normal matter. The antiparticle corresponding to an elementary particle has the same mass as the particle but is opposite in all other properties. The antiparticle corresponding to an electron is a positron, which has the same mass as an electron but a positive charge. Antiprotons have the same mass as protons but a negative charge. When matter and antimatter come together, the two particles annihilate each other, converting their mass into energy or into other types of particles.
Note: As far as scientists can tell, there is almost no naturally occurring antimatter in the universe, although it is possible to make antimatter in particle accelerators.
| antiparticle (ān'tē-pär'tĭ-kəl, ān'tī-) Pronunciation Key
A subatomic particle, such as an antiproton, having the same mass as its corresponding particle, but opposite values of other properties such as charge, parity, spin, and direction of magnetic moment. For example, the antiparticle of the electron is the positron, which has a charge that is equal in magnitude to that of the electron but opposite in sign. Some particles, such as photons, are nondistinct from their antiparticles. When a particle and its antiparticle collide, they may annihilate one other and produce other particles. |
antiparticle
subatomic particle having the same mass as one of the particles of ordinary matter but opposite electric charge and magnetic moment. Thus, the positron (positively charged electron) is the antiparticle of the negatively charged electron. The spinning antineutron, like the ordinary neutron, has a net electric charge of zero, but its magnetic polarity is opposite to that of a similarly spinning neutron. The neutrino, a massless uncharged particle that travels at the speed of light, spins counterclockwise as viewed from behind, whereas the antineutrino spins clockwise as viewed from behind. A particle and its antiparticle mutually react to produce energy by annihilation.
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