Search for evidence ofΛ3nby observingd+π−andt+π−final states in the reaction of6Li+12C at2AGeV

The experimental data obtained from the reaction of ${}^{6}$Li projectiles at 2$A$ GeV on a fixed graphite target were analyzed to study the invariant mass distributions of $d+{\ensuremath{\pi}}^{\ensuremath{-}}$ and $t+{\ensuremath{\pi}}^{\ensuremath{-}}$. Indications of a signal in the $d+{\ensuremath{\pi}}^{\ensuremath{-}}$ and $t+{\ensuremath{\pi}}^{\ensuremath{-}}$ invariant mass distributions were observed with significances of 5.3 $\ensuremath{\sigma}$ and 5.0 $\ensuremath{\sigma}$, respectively, when including the production target, and 3.7 $\ensuremath{\sigma}$ and 5.2 $\ensuremath{\sigma}$, respectively, when excluding the target. The estimated mean values of the invariant mass for $d+{\ensuremath{\pi}}^{\ensuremath{-}}$ and $t+{\ensuremath{\pi}}^{\ensuremath{-}}$ signal were 2059.3 $\ifmmode\pm\else\textpm\fi{}$ 1.3 $\ifmmode\pm\else\textpm\fi{}$ 1.7 MeV/c${}^{2}$ and 2993.7 $\ifmmode\pm\else\textpm\fi{}$ 1.3 $\ifmmode\pm\else\textpm\fi{}$ 0.6 MeV/c${}^{2}$ respectively. The lifetime estimation of the possible bound states yielding to $d+{\ensuremath{\pi}}^{\ensuremath{-}}$ and $t+{\ensuremath{\pi}}^{\ensuremath{-}}$ final states were deduced to be as ${181}_{\ensuremath{-}24}^{+30}\ifmmode\pm\else\textpm\fi{}25$ ps and ${190}_{\ensuremath{-}35}^{+47}\ifmmode\pm\else\textpm\fi{}36$ ps, respectively. Those final states may be interpreted as the two-body and three-body decay modes of a neutral bound state of two neutrons and a $\ensuremath{\Lambda}$ hyperon, ${}_{\ensuremath{\Lambda}}^{\phantom{\rule{0.16em}{0ex}}3}n$.