- a The positron is the antiparticle of the electron. all of whose properties, as mass, spin, or charge, have the same magnitude as but, where appropriate, the opposite sign of a specific ; neutral pions, photons, and gravitons are considered to be their own antiparticles: Compare , .
- any of a group of elementary particles that have the same mass and spin as their corresponding particle but have opposite values for all other nonzero quantum numbers. When a particle collides with its antiparticle, mutual annihilation occurs
- 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.
In, a rare form of that is a mirror image of normal matter. The antiparticle corresponding to an has the same as the particle but is opposite in all other properties. The antiparticle corresponding to an is a , which has the same mass as an electron but a positive . Antiprotons have the same mass as but a negative charge. When matter and antimatter come together, the two particles annihilate each other, converting their mass into or into other types of particles.