Lab frame versus center of momentum frame

[jdstokes]

Why is it conventional to analyse compton scattering in the lab frame (fixed target) whereas all other processes I've seen are analysed in the center of momentum (colliding beam) frame.

Are there any experiments where one would collide electrons with stationary muons e.g.?

 

[Vanadium 50]

Convenience, mostly.

To answer your second question, how do you get stationary muons?

 

[D H]

It is often far easier to analyze things in the center of mass frame. The measurement equipment, however, is in the lab frame, so at some point the results of the analysis have to be recast to the lab frame.

 

[jdstokes]

If the electrons are relativistic then muons confined by electric of magnetic fields could be considered at rest?

 

[jdstokes]

So If I calculate a cross-section in the center of mass frame, is there any way of converting this directly to a Lab cross-section, or do I have to go back to the Feynman amplitude for the process and redo the kinematics at that point.

 

[pam]

You can usually write a cross-section formula in terms of invariants times simple kinematic factors, making going between the cm and the lab relatively easy.

 

[jdstokes]

Ahh yes, the old Mandelstam variables, good point.