(Color online) The real and imaginary parts of the fitted form factor Fπee(s). The black solid and red dashed lines represent our best results of the real and imaginary parts, respectively. The blue dotted and cyan dash-dot-dotted lines correspond to the leading order and the second order contributions of the real parts, respectively. The magenta dash-dotted and green short dash-dash-dotted lines denote the leading order and second order contributions of the imaginary parts.