Isospin decomposition of the photoproduced Σπ system near the Λ(1405)

Recent experimental results for the reaction γ+p→K++Σ+π from CLAS at Jefferson Lab are discussed. It was found that the mass distributions or “line shapes” of the three charge combinations Σ+π−, Σ0π0 and Σ−π+ differ significantly. Our results show that the Λ(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 Σ0π0 channel alone works quite well. The addition of a single I=1 amplitude works fairly well to model all the line shapes simultaneously.