Measurement of ψ(3686)→ΛΛ¯η and ψ(3686)→ΛΛ¯π0 decays

Le résumé fourni par la source

Based on a sample of $448.1\ifmmode\times\else\texttimes\fi{}{10}^{6}\ensuremath{\psi}(3686)$ events collected with the BESIII detector, a study of $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}{\ensuremath{\pi}}^{0}$ and $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}\ensuremath{\eta}$ is performed. Evidence of the isospin-violating decay $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}{\ensuremath{\pi}}^{0}$ is found for the first time with a statistical significance of $3.7\ensuremath{\sigma}$, the branching fraction $\mathcal{B}(\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}{\ensuremath{\pi}}^{0})$ is measured to be $(1.42\ifmmode\pm\else\textpm\fi{}0.39\ifmmode\pm\else\textpm\fi{}0.59)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, and its corresponding upper limit is determined to be $2.47\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 90% confidence level. A partial wave analysis of $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}\ensuremath{\eta}$ shows that the peak around $\mathrm{\ensuremath{\Lambda}}\ensuremath{\eta}$ invariant mass threshold favors a ${\mathrm{\ensuremath{\Lambda}}}^{*}$ resonance with mass and width in agreement with the $\mathrm{\ensuremath{\Lambda}}(1670)$. The branching fraction of the $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}\ensuremath{\eta}$ is measured to be $(2.34\ifmmode\pm\else\textpm\fi{}0.18\ifmmode\pm\else\textpm\fi{}0.52)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. The first uncertainties are statistical and the second are systematic.

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