Everything about Annihilation totally explained
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". Annihilation is the opposite of exnihilation, which means "to create something out of 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 mass. However, high-energy
particle colliders produce annihilations where a wide variety of exotic heavy particles are created.
Examples of annihilation
Kaon to
mix with the antikaon. This is an example of
renormalization in
quantum field theory— the field theory being necessary because the number of particles changes from one to two and back again.
When a low-energy
electron annihilates a low-energy
positron (anti-electron), they can only produce two or more
gamma ray photons, since the electron and positron don't carry enough
mass-energy to produce heavier particles. However, if one or both particles carry a larger amount of kinetic energy, various other particle pairs can be produced. See
electron-positron annihilation.
The annihilation (or decay) of an electron-positron pair into a
single photon, e
+ + e
- → γ, can't occur because energy and momentum wouldn't be conserved in this process. The reverse reaction is also impossible for this reason, except in the presence of another particle that can carry away the excess energy and momentum. However, in
quantum field theory this process is allowed as an intermediate quantum state. Some authors justify this by saying that the photon exists for a time which is short enough that the violation of
energy conservation can be accommodated by the
uncertainty principle. Others choose to assign the intermediate photon a non-zero mass. (The mathematics of the theory are unaffected by which view is taken.) This opens the way for
virtual pair production or annihilation in which a one-particle quantum state may fluctuate into a two-particle state and back again (coherent superposition). These processes are important in the
vacuum state and
renormalization of a quantum field theory. It also allows neutral particle mixing through processes such as the one pictured here.
Further Information
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