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

TL;DR

This paper re-analyzes pion-nucleon differential cross sections from the CHAOS Collaboration, incorporating recent theoretical improvements, and confirms previous findings that question the compatibility of CHAOS data with modern datasets and impact the extraction of the $\sigma$-term.

Contribution

The study introduces refined analysis methods including uncertainty treatment, form factor parameterization, and $\sigma$-meson mass variation, reaffirming earlier conclusions about CHAOS data inconsistencies.

Findings

CHAOS data incompatible with modern datasets

Revised analysis confirms previous doubts about data consistency

Implications for the $\sigma$-term extraction are significant

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.