Stop 2: Simple Two Particle Physics Processes
Using the basic processes shown in Feyman diagrams, one can build a simple set of all basic two-particle processes. Each type of process has a name – often named after the physicist who first described the process.
"Scattering" is a physics term for what happens in a collision – both particles change direction, they exchange some momentum and some energy in the process.
| Name of Process
Description |
Feynman Diagram |
| Compton scattering
electron + photon |
 |
| Bremsstrahlung
electron in medium |
|
| Møller scattering
electron + electron |
 |
| Pair production
photon + photon |
 |
| Pair annihilation
electron + positron |
 |
| Bhabha scattering
electron + positron |
 or  |
A note on conservation of energy and momentum.
- Every actual physical process must respect these laws!
- Every initial and final particle must either be real or come from the matter.
- EGS pictures show only real particles.
You can draw Feynman diagrams that look perfectly reasonable but do not represent possible processes because they are forbidden by conservation of energy or momentum rules.
For example, an isolated single real photon no matter how much energy it has, cannot produce an electron-positron pair that obey these laws. Similarly pair annihilation in vacuum cannot produce just one real photon.
- More about the Conservation Laws.
Go to Stop 3: Sample EGS Images
