What is the connection between path integrals and cross sections?

[earth2]

Hey folks,

i am currently making myself familiar with the path integral in high energy physics by reading Lewis Ryder's QFT book. I do have a question however, since i do not really understand the connection between the path integral and the cross section of a process. Are they only related to each other via the LSZ-reduction formula or is there some other way?

Thanks!
earth2

 

[ansgar]

lsz!