Isospin Decomposition of the Photoproduced \Sigma\pi\ System Near the \Lambda(1405)

TL;DR

This paper analyzes recent CLAS data on \\gamma + p \\to K^+ + \\Sigma + \\pi\ ext{ near the } \\Lambda(1405), revealing the presence of both I=0 and I>0 isospin components in the reaction.

Contribution

It introduces a phenomenological isospin decomposition model that explains the observed line shape differences in the \\Sigma \\pi\ ext{ system near } \\Lambda(1405).

Findings

The \\Lambda(1405) has significant I>0 components.

A two-amplitude Breit-Wigner fit describes the data well.

Including an I=1 amplitude improves the model for all charge states.

Abstract

Recent experimental results for the reaction \gamma + p \to K^+ + \Sigma + \pi\ from CLAS at Jefferson Lab are discussed. It was found that the mass distributions or "line shapes" of the three charge combinations \Sigma^+ \pi^-, \Sigma^0 \pi^0 and \Sigma^- \pi^+ differ significantly. Our results show that the \Lambda(1405), as the I=0 constituent of the reaction, must be accompanied by an I > 0 component. We discuss phenomenological fits to the data to test the possible forms and magnitudes of these amplitudes. A two-amplitude I=0 fit of Breit-Wigner form to the \Sigma^0\pi^0 channel alone works quite well. The addition of a single I=1 amplitude works fairly well to model all the line shapes simultaneously.