Analysis of recent pi(+)p low-energy differential cross-section measurements

The recent pi(+)p differential cross-section measurements between 20 and 100 MeV (pion lab kinetic energy) have been analyzed in the context of an extended threshold expansion of the K matrix. The analysis shows that the bulk of the database is self-consistent. Our results in the S-31 channel disagree with the ones obtained in the Karlsruhe phase-shift analyses (which have been based exclusively on the old pi N database); we report differences of (approximately) one degree in the corresponding phase-shift values and of almost 25% in the s-wave scattering length a(3) (our value: a(3)=-0.077+/-0.003 m(pi)(-1)). These differences reflect the extent of the discrepancy between the old and the new low-energy pi(+)p database; they cannot be attributed to the method of the analysis. A comparison of the present result for the a(3) with the values of the pi N scattering lengths, recently obtained from measurements of the 1 s energy-level shift and width in pionic hydrogen and deuterium, leads to the conclusion that, within the present (experimental and theoretical) accuracies, the various results are not incompatible with the isospin symmetry of the strong interaction.