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

The nature of Lambda(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 pi Sigma isospin channels in the context of chiral dynamics. We have measured the lineshape of Lambda(1405) in charged pi Sigma channels through p(gamma, K+pi)Sigma reaction at 1.5-2.4 GeV. The observed lineshapes are different in terms of pi(-)Sigma(+) and pi(+)Sigma(-) channels, and depends largely on the angular coverage for pions from the A(1405) decay. The cross section for Lambda(1405) photoproduction integrated over the angular region 0.8 < cos(K+)(theta)* < 1.0 was found to be 0.43 mu b in the energy range from 1.5 to 2.0 GeV and 0.072 mu b in the energy range from 2.0 to 2.4 GeV.