Homework Statement
In a 2-body scattering event, A + B → C + D, it is convenient to introduce the Mandelstam variables,
s ≡ −(PA + PB)2 ,
t ≡ −(PA − PC) 2 ,
u ≡ −(PA − PD) 2 ,
where PA,...,D are the 4-momenta of the particles A, . . . , D respectively, (· · ·) 2 = (· · ·) · (· · ·) denotes a...