Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil (nothing). A literal translation is "to make into nothing". In physics, the word is used to denote the process that occurs when a subatomic particle collides with its respective antiparticle. Since energy and momentum must be conserved, the particles are not actually made into nothing, but rather into new particles. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of the original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.

During a low-energy annihilation, photon production is favored, since these particles have no rest mass. However, high-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created.

Examples of annihilation

• When a low-energy electron annihilates a low-energy positron (anti-electron), it yields gamma rays only, since these particles do not carry enough mass-energy to produce heavier particles. See electron-positron annihilation.

• The single-photon annihilation of an electron-positron pair, e⁺  +  e^-  →  γ cannot occur because it is impossible to conserve energy and momentum together in this process. The reverse reaction is also impossible for this reason. However, in quantum field theory this process is allowed as an intermediate quantum state for times short enough that the violation of energy conservation can be accommodated by the uncertainty principle. This opens the way for virtual pair production or annihilation in which a one particle's quantum state may fluctuate into a two particle state and back again. These processes are important in the vacuum state and renormalization of a quantum field theory. It also opens the way for neutral particle mixing through processes such as the one pictured on the right, which is an example of mass renormalization.

Particle physics

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