There isn't a text and the notes the instructor gave are incomplete. He started to explain it, then went off on a tangent and never explained how we are to approach this problem. He has tried to turn this junior level course into an upper level graduate course.
Homework Statement
Calculate the differential cross section for A+B---> C+D with an invariant matrix element
Homework Equations
See attachment
The Attempt at a Solution
I have no idea how to even begin this problem. The course I am taking is an undergraduate course in intermediate modern...