Complex amplitude phase motion in Dalitz plot heavy meson three body decay

We propose a method to determine the phase motion of a complex amplitude in three body heavy meson decays. We show that the phase variation of a complex amplitude can be directly revealed through the interference observed in the Dalitz plot region where it crosses with a well established resonant state. This method could be applied to the decays D+→π−π+π+ and D+→K−π+π+, to determine whether the low mass states σ and κ, suggested by E791, have phase motions compatible with resonances.