New analysis of the low-energy $π^\pm p$ 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 ($πN$) differential cross sections (DCSs) of the CHAOS Collaboration and came to the conclusion that the angular distribution of their $π^+ p$ 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 $πN$ amplitude, and the inclusion of the effects of the variation of the $σ$-meson mass when fitting the ETH model of the $πN$ interaction to the experimental data. The new analysis of the CHAOS DCSs confirms our earlier conclusions and casts doubt on the value for the $πN$ $Σ$ term, which Stahov, Clement, and Wagner have extracted from these data.

19 pages, 2 figures, 1 table