Phase Motion in the Scalar Low-Mass pi+pi- Amplitude in D+ -> pi-pi+pi+   Decay
  Applying the Amplitude Difference method to Fermilab experiment E791 D+ -> pi-pi+pi+ data, we measure the low mass pi+pi- phase motion. Our results suggest a significant phase variation, compatible with the existence of an isoscalar sigma(500) meson, as previously reported using an isobar model fit to the full Dalitz-plot density. 
Ignacio Bediaga and Jussara M. de Miranda