A proton with momentum 3 GeV in LAB frame of reference is difussed elastically by a stationary proton. The angle of diffusion of one of the protons, in the CM system is 10º, corresponding to a moment fo 2.982GeV in LAB.
This is part of an exam problem, it then goes on to ask about energy, momentum and angle in both frames.
The doubt I have is conceptual: ¿How can there be an angle of diffusion in the CM frame? naively, I guess, one would expect the collision to be heads on in the CM frame, why is this not the case?