${{\boldsymbol \Lambda}{(1405)}}$ $I(J^P)$ = $0(1/2^{-})$ 

In the 1998 Note on the ${{\mathit \Lambda}{(1405)}}$ in PDG 1998 , R.H. Dalitz discussed the S-shaped cusp behavior of the intensity at the ${{\mathit N}}-{{\overline{\mathit K}}}$ threshold observed in THOMAS 1973 and HEMINGWAY 1985 . He commented that this behavior "is characteristic of ${\mathit S}{\mathrm -wave}$ coupling; the other below threshold hyperon, the ${{\mathit \Sigma}{(1385)}}$, has no such threshold distortion because its ${{\mathit N}}-{{\overline{\mathit K}}}$ coupling is ${\mathit P}{\mathrm -wave}$. For ${{\mathit \Lambda}{(1405)}}$ this asymmetry is the sole direct evidence that $\mathit J{}^{P} = 1/2{}^{-}$." A recent measurement by the CLAS collaboration, MORIYA 2014 , definitively established the long-assumed $\mathit J{}^{P} = 1/2{}^{-}$ spin-parity assignment of the ${{\mathit \Lambda}{(1405)}}$. The experiment produced the ${{\mathit \Lambda}{(1405)}}$ spin-polarized in the photoproduction process ${{\mathit \gamma}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit K}^{+}}{{\mathit \Lambda}{(1405)}}$ and measured the decay of the ${{\mathit \Lambda}{(1405)}}$ (polarized) $\rightarrow$ ${{\mathit \Sigma}^{+}}$ (polarized) ${{\mathit \pi}^{-}}$ . The observed isotropic decay of ${{\mathit \Lambda}{(1405)}}$ is consistent with spin $\mathit J = 1/2$. The polarization transfer to the ${{\mathit \Sigma}^{+}}$(polarized) direction revealed negative parity, and thus established $\mathit J{}^{P} = 1/2{}^{-}$.