# What is Pair annihilation: Definition and 14 Discussions

In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an 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.
The word "annihilation" takes use informally for the interaction of two particles that are not mutual antiparticles – not charge conjugate. Some quantum numbers may then not sum to zero in the initial state, but conserve with the same totals in the final state. An example is the "annihilation" of a high-energy electron antineutrino with an electron to produce a W−.
If the annihilating particles are composite, such as mesons or baryons, then several different particles are typically produced in the final state.
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1. ### I Deriving the relativistic rocket equation with exhaust efficiency

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2. ### B How many nuclear weapons are needed to make a wormhole?

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I have read on Wikipedia (https://en.wikipedia.org/wiki/Compton_wavelength) that we cannot measure the position of a particle more precise than half of its Compton wavelength, since the photon we would need will be so energetic to produce electron-positron pairs. How does the creation of...
4. ### Quantum Pair Production QED: Finding a Study Guide

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5. ### B Entanglement and pair-production and annihilation

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6. ### A Electron-positron pair annihilation

Consider the following u-channel diagram (on the right) in the link below. https://www.physicsforums.com/attachments/diphoton-png.95147/ Let the polarization vectors of ##k_1## and ##k_2## be ##(\epsilon^{\mu}_{1})^{*}## and ##(\epsilon^{\mu}_{2})^{*}## respectively. Do you label the incoming...
7. ### Feynman diagram for pair annihilation

Hi, I've been reading about Feynman diagrams lately and I'm trying to understand the pair annihilation diagram. The picture's here: http://en.wikipedia.org/wiki/File:Feynman_EP_Annihilation.svg I don't understand the following things about the diagram: 1. Why anti-patricles have to...
8. ### Pair production and pair annihilation

what are pair production and pair annihilation phenomena?
9. ### Silly question about pair annihilation

Hi all. I have a (probably stupid) question about e^{+}e^{-} annihilation. I was reading about the emission of two 511keV photons which is the electron's mass. But, is this energy fixed every time e^{+}e^{-} annihilates in a two photons or is just the energy of the positronium dacay? My idea...
10. ### Delay of virtual particle pair annihilation

My grasp of physics is limited, however, I am an engineer, thus I am asking for other's assistance in understanding how to delay the annihilation of a virtual particle pair. Most literature I've read, indicates a virtual particle pair is "real" if only briefly. QUESTION: How long is...
11. ### Can Particle Pair Annihilation Produce Only One Photon?

1. Problem Statement What is the wavelength of each of the two photons produced when a particle pair of a positron and electron accelerated at 25GeV collide? Can the net result of this annihilation be only ONE single photon? Why or why Not? Homework Equations Etotal(initial) =...
12. J

### Pair Annihilation and Conservation of Momentum and Energy Explained

I'm a little unsure about a certain part of this shown in a book. There is an electron and a positron moving in the +x direction. They annihilate each other and release 2 photons. to conserve momentum 1 moves in the -x and one in the +x direction. So then the first step is to do conservation...
13. ### Electric fields of electron and positron that undergo pair annihilation.

Here is a question, which may seem dumb: Consider an electron and a positron that annihilate, both of which are non-relativistic (taking the observer's frame of reference to be the center of mass frame of the electron-positron pair) so that we only consider their electric fields for simplicity...
14. ### How to Solve a Pair Annihilation Problem for the Energy of Resulting Particles?

Does anyone know how to solve a pair annihilation problem ( positron and electron), for the energy of the resulting particles, in this case photons?