Systematic effects in the low-energy behavior of the current SAID solution for the pion-nucleon system

Abstract

We investigate the description of the pion-nucleon experimental data at low energy (i.e., below pion laboratory kinetic energy of 100[Formula: see text]MeV) on the basis of the current SAID solution (WI08). We demonstrate that, in a self-consistent analysis scheme, the scale factors of the fits based on the Arndt–Roper formula come out independent of the beam energy and ‘cluster’ around the expectation value of [Formula: see text]. We report systematic effects in the low-energy behavior of the WI08 solution. These effects indicate that at least one of the three following assumptions, underlying the WI08 analysis, does not hold, namely that: (a) the bulk of the data is reliable, (b) the electromagnetic effects are correctly accounted for and (c) the isospin invariance in the strong interactions of the [Formula: see text] system is valid.