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

TL;DR

This paper analyzes low-energy pion-proton scattering data from the CHAOS Collaboration, finding issues with the angular distribution shapes that hinder model parameter extraction and highlighting challenges in interpreting these measurements.

Contribution

It provides a detailed analysis of CHAOS low-energy pion-proton scattering data and identifies specific issues with the angular distribution shapes affecting model fitting.

Findings

Outliers were removed from the dataset.

Standard low-energy parameterizations were initially used.

The ETH model fitting failed to produce reasonable parameters.

Abstract

This paper presents the results of an analysis of the low-energy $\pi^\pm p$ differential cross sections, acquired by the CHAOS Collaboration at TRIUMF \cite{chaos,denz}. We first analyse separately the $\pi^+ p$ and the $\pi^- p$ elastic-scattering measurements on the basis of standard low-energy parameterisations of the $s$- and p-wave $K$-matrix elements. After the removal of the outliers, we subject the truncated $\pi^\pm p$ elastic-scattering databases into a common optimisation scheme using the ETH model \cite{glmbg}; the optimisation failed to produce reasonable values for the model parameters. We conclude that the problems we have encountered in the analysis of these data are due to the shape of the angular distributions of their $\pi^+ p$ differential cross sections.