Phase Motion in the Scalar Low-Mass $π^-π^+$ Amplitude in $D^+ \to π^-π^+π^+$

Abstract

This work is a direct and model-independent measurement of the low mass $π^+π^-$ phase motion in the $D^+ \to π^-π^+π^+$ decay. The results show a strong phase variation, compatible with an isoscalar $σ(500)$ meson. This result confirms the previous Fermilab E791 result which found evidence for the existence of this scalar particle using a full Dalitz-plot analysis.