Hyperon III: \(K^{-}p - \pi \varSigma \) coupled-channel dynamics in the \(\varLambda (1405)\) mass region

Low-energy data on the three charge states in $$\gamma p \rightarrow K^+(\varSigma \pi )$$ from CLAS at JLab, on $$K^-p\rightarrow \pi ^0\pi ^0\varLambda $$ and $$\pi ^0\pi ^0\varSigma $$ from the Crystal Ball at BNL, bubble chamber data on $$K^-p\rightarrow \pi ^-\pi ^+\pi ^{\pm }\varSigma ^{\mp }$$ , low-energy total cross sections on $$K^-$$ induced reactions, and data on the $$K^-p$$ atom are fitted with the BnGa partial-wave-analysis program. We find that the data can be fitted well with just one isoscalar spin-1/2 negative-parity pole, the $$\varLambda (1405)$$ , and background contributions. In a fit with one isocsalar state, the $$\varLambda (1405)$$ structure can be determined as a dominantly SU(3) singlet state. A fit with two isoscalar singlet states, with imposed properties of the low-mass state, is, however, also not incompatible with data.