To solve the current debate on the position of the quasibound $K^{-}p$ state, namely, “$\Lambda (1405)$ or $\Lambda {}^{*}(1420),$” we propose to measure the $T_{21}=T_{\Sigma \pi \leftarrow \mathrm{K̄}N}$ $\Sigma \pi$ invariant-mass spectrum in stopped-$K^{-}$ absorption in the deuteron, since the spectrum, reflecting the soft and hard deuteron momentum distribution, is expected to have a narrow quasifree component with an upper edge of $M=1430$ MeV/$c^2$, followed by a significant “high-momentum” tail toward the lower mass region, where a resonant formation of $\Lambda (1405)$ of any mass and width in a wide range will be clearly revealed. We introduce a “deviation” spectrum as defined by $\mathrm{DEV}$ $=$ $\mathrm{OBS}$ (observed or calculated) / $\mathrm{QF}$ (nonresonant quasifree), in which the resonant component can be seen as an isolated peak free from the QF shape.

• Received 17 March 2011

DOI:https://doi.org/10.1103/PhysRevC.83.055207