In a high energy physics experiment, do you ever scatter more than 2 particles at a time? Suppose you scatter 4 incoming particles and get 4 outgoing particles. Do you only look at connected diagrams with 8 external lines? Or do you also have to take into account the product of disconnected graphs with 4 external lines? I know a beam of particles is used, but do the particles in the beam collide one at a time with the target, or can two particles in the beam collide at the same time with the target?