A formulation for description of pi^+(2pi^-) and pi^-(2pi^+) channels in Bose-Einstein correlation by Coulomb wave function

In order to analyze data on charged pions correlation channels, pi^+(2pi^-) and pi^-(2pi^+), we propose new interferometry approach using the Coulomb wave function. We show that to describe adequately data we have to introduce new parameter describing the contribution of pi^-(k_1) pi^+(k_2) --> pi^-(k_2) pi^+(k_1) process. Using this new formula we analyze data on pi^+(2pi^-) and pi^-(2pi^+) channels at sqrt(s) = 91 GeV by DELPHI Collaboration, and estimate the magnitude of this new parameter as well as the degree of coherence.