On the significance of the neutron-electron scattering length measurements

According to Yukawa meson theory the neutron has to possess a spatial charge distribution. The 'tail' of this distribution has to be negative since virtual negative pion is the reason of the tail. Therefore the neutron mean square intrinsic charge radius <r sub E sub , sub i sub n sup 2 >, has also to be negative. From the measurements of the neutron-electron scattering length at low energy one can obtain the information about the value and the sign of <r sub E sub , sub i sub n sup 2 >. But there are series of experiments obtaining <r sub E sub , sub i sub n sup 2 > >0, in contradiction with Yukawa theory.