Measurements ofJ/ψandψ(2S)decays intoΛΛ¯π0andΛΛ¯η

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Abstract

Using $58\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $J/\ensuremath{\psi}$ and $14\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $\ensuremath{\psi}(2S)$ events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{0}$ and $\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}\ensuremath{\eta}$ are measured. For the isospin violating decays, the upper limits are determined to be $\mathcal{B}(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{0})<6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and $\mathcal{B}[\ensuremath{\psi}(2S)\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{0}]<4.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ at the 90% confidence level. The isospin conserving process $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}\ensuremath{\eta}$ is observed for the first time, and its branching fraction is measured to be $\mathcal{B}(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}\ensuremath{\eta})=(2.62\ifmmode\pm\else\textpm\fi{}0.60\ifmmode\pm\else\textpm\fi{}0.44)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, where the first error is statistical and the second one is systematic. No $\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}\ensuremath{\eta}$ signal is observed in $\ensuremath{\psi}(2S)$ decays, and $\mathcal{B}[\ensuremath{\psi}(2S)\ensuremath{\rightarrow}\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}\ensuremath{\eta}]<1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ is set at the 90% confidence level. Branching fractions of $J/\ensuremath{\psi}$ decays into ${\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\overline{\ensuremath{\Lambda}}$ and ${\overline{\ensuremath{\Sigma}}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}\ensuremath{\Lambda}$ are also reported, and the sum of these branching fractions is determined to be $\mathcal{B}(J/\ensuremath{\psi}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\overline{\ensuremath{\Lambda}}+\mathrm{c}.\mathrm{c}.)=(1.52\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.16)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.

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