Nucleon Form Factors in the Helicity Representation

The cross section for electron-nucleon scattering should be expressed in terms of form factors which are proportional to helicity amplitudes. Then electron-nucleon scattering and pion-nucleon scattering are related even more closely by the $\pi -\pi$ interaction in $I=1\mathrm{}$, $J=1\mathrm{}$. In particular the $S$-wave charge-exchange scattering data complement data on the electric isovector form factor. A consistent picture of the $I=1\mathrm{}$, $J=1\mathrm{}$ $\pi -\pi$ interaction requires the narrowness of the 750-MeV resonance.