The pion nucleon coupling constant

The latest \({\rm\pi} N\) elastic scattering data are re-analysed to determine the coupling constant gc of the charged pion, using the dispersion relation for the invariant amplitude B(+ ). Depending on the choice of data-base, values \(g^2_c/4{\rm\pi} = 13.80\) to 13.65 are obtained with errors of \(\pm 0.12\). The mass difference between charge states of \(\Delta (1232)\) is \(M^0 -M^{ + + } = 2.0 \pm 0.4\) MeV, close to twice the mass difference between neutron and proton. The difference in widths on resonance is \(\Gamma^0 - \Gamma^{ + + } = 3.8 \pm 1.0\) MeV. One may account for a width difference of 4.5 MeV from phase space for decays and the extra channel \(\Delta^0 \to \gamma n\).