New analysis of the low-energy $\pi^\pm p$ differential cross sections of the CHAOS Collaboration

Abstract

In a previous paper, we reported the results of a partial-wave analysis of the pion-nucleon ($\pi N$) differential cross sections (DCSs) of the CHAOS Collaboration and came to the conclusion that the angular distribution of their $\pi^+ p$ data sets is incompatible with the rest of the modern (meson-factory) database. The present work, re-addressing this issue, has been instigated by a number of recent improvements in our analysis, namely regarding the inclusion of the theoretical uncertainties when investigating the reproduction of experimental data sets on the basis of a given `theoretical' solution, modifications in the parameterisation of the form factors of the proton and of the pion entering the electromagnetic part of the $\pi N$ amplitude, and the inclusion of the effects of the variation of the $\sigma$-meson mass when fitting the ETH model of the $\pi N$ interaction to the experimental data. The new analysis of the CHAOS DCSs confirms our earlier conclusions and casts doubt on the value for the $\pi N$ $\Sigma$ term, which Stahov, Clement, and Wagner have extracted from these data.