The Peak Structure in the In-Flight ${}^3\text{He}(K^{-},\mathrm{\Lambda }p)n$ Reaction Around the $\bar{K}NN$ Threshold

We theoretically investigate the origin of the peak structure around the $K^{-}pp$ threshold observed in the in-flight ${}^{3}$\text{He}$ ( K^{-} , , \Lambda p ) n$ reaction in the recent E15 experiment at J-PARC. For this purpose, we consider two scenarios to produce the peak. One is that the $\mathrm{\Lambda }(1405)$ is generated but it does not correlate with $p$, and the uncorrelated $\mathrm{\Lambda }(1405)p$ system subsequently decays into $\mathrm{\Lambda }p$. The other one is that the $\bar{K}NN$ bound state is indeed generated and decays into $\mathrm{\Lambda }p$. As a result, the experimental signal is qualitatively well reproduced in the $\bar{K}NN$ bound scenario, definitely discarding the uncorrelated $\mathrm{\Lambda }(1405)p$ one.