${{\mathit \Lambda}}$ BARYONS($\mathit S$ = $-1$, $\mathit I$ = 0) ${{\mathit \Lambda}^{0}}$ = ${\mathit {\mathit u}}$ ${\mathit {\mathit d}}$ ${\mathit {\mathit s}}$

#### ${{\mathit \Lambda}{(1405)}}$

$I(J^P)$ = $0(1/2^{-})$
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 $\mathit J{}^{P} = 1/2{}^{-}$.
 See related review: Pole Structure of the ${{\mathit \Lambda}{(1405)}}$ Region
${{\mathit \Lambda}{(1405)}}$ POLE POSITION
 REAL PART
 $-2{\times }$IMAGINARY PART
${{\mathit \Lambda}{(1405)}}$ MASS
 PRODUCTION EXPERIMENTS $1405.1 {}^{+1.3}_{-1.0}$ MeV
 EXTRAPOLATIONS BELOW ${{\mathit N}}{{\overline{\mathit K}}}$ THRESHOLD
${{\mathit \Lambda}{(1405)}}$ WIDTH
 PRODUCTION EXPERIMENTS $50.5 \pm2.0$ MeV
 EXTRAPOLATIONS BELOW ${{\mathit N}}{{\overline{\mathit K}}}$ THRESHOLD
 $\Gamma_{1}$ ${{\mathit \Sigma}}{{\mathit \pi}}$ 100$\%$ 155
 $\Gamma_{2}$ ${{\mathit \Lambda}}{{\mathit \gamma}}$ 260
 $\Gamma_{3}$ ${{\mathit \Sigma}^{0}}{{\mathit \gamma}}$ 196
 $\Gamma_{4}$ ${{\mathit N}}{{\overline{\mathit K}}}$ -1
 FOOTNOTES