The Nucleus Resolved, Ch Reactions: four-vectors, amplitudes and partial waves
Problem
A beam of 7Li ions (mass number A=7) is fired at a stationary hydrogen (proton) target and scatters elastically. In the centre-of-mass frame the scattering is isotropic.
((a)) Predict the maximum laboratory angle at which a scattered 7Li ion can be observed, treating the mass ratio as the ratio of mass numbers.
((b)) A second experiment fires protons at a stationary 7Li target, producing the same reaction run in the opposite kinematic sense, at the same centre-of-mass energy. Without doing a calculation, state whether the total cross section measured in that experiment must equal the one for the first (beam-and-target-reversed) experiment, and give the reason.