Measurement of the mesonic decay branch of the K̄\!N\!N quasi-bound state

We conducted measurements of K⁻ + ³ He → π \!Y \!N + N' reactions using 1~ GeV/c K⁻-beam, aiming to understand the broad decay width of K̄ \!N \!N (≈ twice as broad as that of Λ(1405) considered to be the K̄ \!N quasi-bound state). We successfully reproduced distributions of the π \! Y \! N invariant mass and momentum transfer of π \! Y \! N by employing model fitting functions for K̄ \! N \! N formation and quasi-free K̄ absorption (QF_K̄- abs) processes. The model can describe the experimental data quite well, and four K̄ \! N \! N → π \! Y \! N cross-sections were obtained. The result suggests that the mesonic decay is the dominant decay branch of K̄ \! N \! N. It was also suggested that Γπ Λ N ~ Γπ Σ N, which indicates a significant contribution of the IK̄ \! N=1 absorption channel to the K̄ \! N \! N decay as well as the IK̄ \! N=0 makes the K̄ \! N \! N state ≈ twice as unstable as Λ(1405).