Description of interference in hadron and parton showers by Laplace method

We apply Laplace method for the tree diagrams to calculate the interference terms arising as a result of summation of particles permutations in the final state of scattering. These terms significantly influence the values of experimentally observed quantities. We show that the tree diagram with a single input line and an arbitrary number of output lines has a maximum value for the equal four-momenta of secondary particles. It means the tree diagrams of inelastic scattering describe the formation of parton and hadron showers. We also demonstrate the need to take into account the contributions from interference between different showers.