# Positron-Electron Annihilation - two questions

1. Feb 4, 2005

### what_are_electrons

At the colliders, positrons and electrons are accelerated at MeV, GeV levels on their way to making head-on collisions. Various Bosons can be produced. The most discussed type seems to be the two Gamma Photons (511 keV). Question #1: What happens to the XS energy of the positrons and electrons after they have been "converted" into the two gamma photons?

When I use SLAC's EGS software which has an upper limit of 200 MeV for accelerating positrons, I use liquid hydrogen as the target and look at the results, which include gamma ray emission, electron emission and positron scattering, but none of the other possible bosons. I have used as few as 10 positrons and the max of 100 positrons in the simulation, but I see only about a 10% production of gamma rays. Question #2. What am I overlooking?

2. Feb 4, 2005

### anti_crank

The excess energy is transmitted to the photons in this case, ergo the photons' energy will be much, much larger than simply 511keV. That number, by the way, applies to the annihilation of an electron-positron that are both at rest.

Last edited: Feb 4, 2005
3. Feb 4, 2005

4. Feb 6, 2005

### Staff: Mentor

http://www.pparc.ac.uk/Rs/Pp/Sp/Artcl/LEP.asp

Also, check out the pdf file at Feynman Diagrams and Electron-Positron Annihilation It's a good overview.

Particles occur above some energy threshold (the rest mass), i.e. the total energy involved must exceed the rest energy of the particle that is to be created.

Last edited by a moderator: May 1, 2017
5. Feb 6, 2005

6. Feb 6, 2005