Abstract
Low-energy data on the three charge states in gamma p rightarrow K^+(varSigma pi ) from CLAS at JLab, on K^-prightarrow pi ^0pi ^0varLambda and pi ^0pi ^0varSigma from the Crystal Ball at BNL, bubble chamber data on K^-prightarrow 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.
Highlights
Ied the S-wave K N interactions in a relativistic chiral unitary approach based on a chiral Lagrangian
HADES data on the reaction p + p → Σ+ + π − + K + + p were successfully fitted with a single Λ(1405) at 1380 MeV [27]; it was shown that the peak cannot be assigned to Σ(1385)
The peak structure in the data was assigned to a single pole, while the second one provided a continuum background amplitude affecting the shape of the peak, but that pole was not interpreted as genuine resonance
Summary
HADES data on the reaction p + p → Σ+ + π − + K + + p were successfully fitted with a single Λ(1405) at 1380 MeV [27]; it was shown that the peak cannot be assigned to Σ(1385). This result was criticized in a subsequent reanalysis [28] where the mass was determined to 1405+−191 MeV. The peak structure in the data was assigned to a single pole, while the second one provided a continuum background amplitude affecting the shape of the peak, but that pole was not interpreted as genuine resonance. A solution with two lowmass isoscalar poles describes the data with similar precision
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