A process in which a particle meets its corresponding antiparticle and both disappear. Their energy and momentum appears in some other form, producing other particles together with their antiparticles and providing their motion.
The process whereby a particle and its antiparticle interact, converting their mass into energy, according to Einstein's famous formula, E = mc2. For example, the annihilation of an electron and positron results in the emission of photons with an energy of 511 k eV.
spontaneous conversion of a particle and its anti-particle into radiation. e.g. positron and electron into two gamma-ray photons of energy 511 keV
A process in which a particle meets its corresponding antiparticle and both disappear. The energy appears in some other form, perhaps as a different particle and its antiparticle (and their energy), perhaps as many mesons, perhaps as a single neutral boson such as a 0 boson. The produced particles may be any combination allowed by conservation of energy and momentum and of all the charge types and other rules.
Annihilation of particles is the disappearance of the mass energy of a particle and its corresponding antiparticle, and its appearance as another sort of energy (possibly including a spray of particles of total quantum number zero for each of the additive quantum numbers).