The Nature of the Λ(1405) from Photoproduction at SPring-8/LEPS

The nature of Λ (1405) hyperon is yet unresolved for distinction among three-quark state, meson-baryon molecular state, or any other new form of hadronic matter. Recent theoretical works predict its lineshape to be different in terms of the πΣ isospin channels in the context of chiral dynamics. We have measured the lineshape of Λ (1405) in charged πΣ channels through p (γ, K⁺ π) Σ reaction at 1.5-2.4 GeV. The observed lineshapes are different in terms of π^- Σ⁺ and π⁺ Σ^- channels, and depends largely on the angular coverage for pions from the Λ (1405) decay. The cross section for Λ (1405) photoproduction integrated over the angular region 0.8 < cos θ_K+^* < 1.0 was found to be 0.43μb in the energy range from 1.5 to 2.0 GeV and 0.072μb in the energy range from 2.0 to 2.4 GeV.