Discrepancies between πN charge exchange forward scattering data and the dispersion relation prediction
The πN charge-exchange forward scattering amplitude has been recalculated, using the most recent total cross section data, charge independence and the forward dispersion relation. In general the prediction agrees rather well with the data, but there are several discrepancies which are considerably larger than the errors. Some of these discrepancies follow from the fact that a structure at small ¦t¦ has been ignored in the extrapolation. — The new fit gives an accurate value for the subtraction constant of the integral. It agrees with the evaluation of the unsubtracted integral at threshold, if, at high energies, the Regge behaviour for σ(π−p)—σ(π+p) is inserted. This result favours the validity of Pomeranchuk's theorem. — An improved value forf2 cannot be obtained at present because of the uncertainty following from charge-dependent effects at low energies.