Antiparticle

There is an antiparticle corresponding to most kinds of particle. It has the same mass and opposite electric charge.^[1]

Even electrically neutral particles, such as the neutron, are not identical to their antiparticle. In the example of the neutron, the 'ordinary' particle is made out of quarks and the antiparticle out of antiquarks.^[2]

Particle-antiparticle pairs can annihilate each other if they are in appropriate quantum states. They can also be produced in various processes. These processes are used in particle accelerators to create new particles and to test theories of particle physics. High energy processes in nature can create antiparticles. These are visible in cosmic rays and in certain nuclear reactions. The word antimatter properly refers to (elementary) antiparticles, composite antiparticles made with them (such as antihydrogen) and to larger assemblies of either.

1. ↑ The exceptions are massless bosons such as the photon and the graviton.
2. ↑ The laws of nature were thought to be symmetric between particles and antiparticles until CP violation experiments found that time-reversal symmetry is violated in nature. This small asymmetry is involved in baryogenesis, how our universe came to consist almost entirely of matter, with almost no free antimatter.