Scalar meson sigma phase motion at D+-> pi- pi+pi+ decay

We make a direct and model-independent measurement of the low pi+ pi- mass phase motion in the D+ ® p-pi+pi+ decay. Our preliminary results show a strong phase variation, compatible with the isoscalar sigma(500) meson. This result confirms our previous result [1] where we found evidence for the existence of this scalar particle using full Dalitz-plot analysis. We apply the Amplitude Difference (AD) method [2] to the same Fermilab E791 data sample used in the preceding analysis. We also give an example of how we extract the phase motion of the scalar amplitude, looking...