In lowest order, the process e⁺+ e^-†’ μ⁺+ μ^-is given by the Feynman diagram of Figure 1.16. Estimate the typical distance between the vertices at energies much larger than the masses of any of the particles in (a) the rest frame of the electron and (b) the centre-of-mass frame. Check the consistency of these estimates by considering the Lorentz contraction in going from the rest frame, in which the initial electron is stationary, to the centre-of-mass frame.

Figure 1.16 Lowest-order diagram for et +e t + .