Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Possible electron-positron annihilation products?

Learn more physics!

Most recent answer: 06/23/2010
Q:
From what I understand, events like the following can and do occur: electrons and positrons can annihilate one another, resulting in the formation photons, and these can reappear as other elementary particles, perhaps not even leptons. (1) Why do electrons and positrons annihilate one another? (2) Why does this result in the emergence of photons? And, more generally, (3) why can one kind of elementary particle transmute into another kind of elementary particle (e.g. electron/positron --> photons --> quarks/antiquarks? What's the "mechanism"?
- Vito
Baltimore, MD USA
A:
This is a very interesting question as it brings into focus some profound properties of particle interactions.  The usual products of electron-positron annihilation are photons; sometimes two and sometimes three.  The standard explanation for this is that photons are the carriers of electromagnetic interactions and using the rules that Feynman devised for quantum electrodynamics one can calculate these rates.  However, from time to time other particles are seen that are usually associated with the weak interactions.  The LEP accelerator at CERN which collides high energy electrons and positrons observed W and Z bosons, carriers of the weak force that mediates, for example, β decay of nuclei. This and many other experiments indicated that the electromagnetic and weak interactions are somehow mixed together.  So what's going on?   Salam, Glashow, and Weinberg eventually figured it out and shared a Nobel Prize for their efforts in developing the electro-weak theory, a unification of the electromagnetic and weak interactions. As such, the W and Z bosons can then couple to quarks and anti-quarks. It's pretty tricky but look at: 
  for more information.

LeeH

(published on 06/23/2010)

Follow-up on this answer.