Two particle into two particle scattering is a common topic in the field of particle physics and is studied so often that special notation has been developed to facilitate discussion of such processes. The convention uses the "so-called" Mandelstam variables (s,t,u) where (p_i) represents the momentum of the four particles (
):
These variables completely describe the momentum space of the problem in a Lorentz invariant way. One of the useful properties of this choice of variables is the fact that:
Furthermore we can elucidate these conditions by drawing the corresponding Feynman diagrams for each process.
s-channel
t-channel
u-channel
