Lineshape of the Λ(1405)Λ(1405) hyperon measured through its Σ0π0Σ0π0 decay

The pp→pK+Y0pp→pK+Y0 reaction has been studied for hyperon masses m(Y0)⩽1540 MeV/c2m(Y0)⩽1540 MeV/c2 at COSY-Jülich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Λ   and Σ0Σ0 hyperons as well as the Σ0(1385)Σ0(1385) and Λ(1405)Λ(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well separated, though with limited statistics. The shape and position of the Λ(1405)Λ(1405) distribution, reconstructed cleanly in the Σ0π0Σ0π0 channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Λ(1405)Λ(1405) to be a two-state resonance.