# Angular momentum in particle interaction

1. Nov 5, 2013

### johne1618

Imagine that two electrons interact by exchanging a virtual photon.

Electron A gains momentum $-\vec{p}$ and electron B gains momentum $\vec{p}$.

If the two momentum vectors are not collinear then there will be extra angular momentum left over from the interaction.

In a simple Coulomb interaction the momenta of A and B are collinear but I would have thought that in a general interaction they would not be. In that case how would angular momentum be conserved?

PS As the photon is virtual there isn't anything left in the EM field.

2. Nov 5, 2013

### Staff: Mentor

Why do you think that?

3. Nov 5, 2013

### johne1618

I can only think in classical terms using the Lienard-Wiechert theory.

If electron A has an acceleration perpendicular to the line A-B then electron B will receive some momentum perpendicular to A-B opposite A's acceleration.

Therefore the total momentum, $\vec{p}$, transferred to B will not be parallel to A-B.