Lessons from fitting the lowest order energy independent chiral based $\bar{K}N$ potential to experimental data

TL;DR

This paper investigates how fitting a simple, energy-independent chiral-based $ar{K}N$ potential to various experimental data sets affects the physical conclusions about the system, revealing tensions between different data types.

Contribution

It demonstrates the impact of data selection on the fitted potential parameters and the resulting physical interpretations in the $ar{K}N$ interaction model.

Findings

Fitting to different data sets yields conflicting pole positions.

Reproducing all data simultaneously with a simple potential is challenging.

Certain pole positions are resistant to fitting across all data sets.

Abstract

It is shown, that fitting parameters of a $\bar{K}N$ interaction model to different sets of experimental data can lead to physical conclusions which might provide a deeper insight into the physics of this multichannel system. The available experimental data are divided into three parts: the "classical" set consisting of the low-energy $K^-p$ cross sections and the threshold branching ratios, the SIDDHARTA $1s$ level shift in kaonic hydrogen and the CLAS photoproduction data. We have fitted the parameters of the potential to different combinations of these data. We found, that the two poles corresponding to the $I=0$ nuclear quasi-bound state ($\Lam$) and to the $K^-p$ $1s$ atomic level seem to resist to their simultaneous reproduction at the right place, though a more or less satisfactory compromise can be achieved. Potentials with the $\Lam$ pole pinned down close to the PDG value fail to reproduce the classical two-body data with an acceptable accuracy. We also added comments on two papers criticizing the potential used in the fits.