Study of electromagnetic Dalitz decays χcJ→μ+μ−J/ψ

Le résumé fourni par la source

Using $4.48\ifmmode\times\else\texttimes\fi{}{10}^{8}\text{ }\text{ }\ensuremath{\psi}(3686)$ events collected with the BESIII detector, we search for the decays ${\ensuremath{\chi}}_{cJ}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi}$ through the radiative decays $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{cJ}$, where $J=0$, 1, 2. The decays ${\ensuremath{\chi}}_{c1,2}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi}$ are observed, and the corresponding branching fractions are measured to be $\mathcal{B}({\ensuremath{\chi}}_{c1}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi})=(2.51\ifmmode\pm\else\textpm\fi{}0.18\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\mathcal{B}({\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi})=(2.33\ifmmode\pm\else\textpm\fi{}0.18\ifmmode\pm\else\textpm\fi{}0.29)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, where the first uncertainty is statistical and the second one systematic. No significant ${\ensuremath{\chi}}_{c0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi}$ decay is observed, and the upper limit on the branching fraction is determined to be $2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ at 90% confidence level. Also, we present a study of dimuon invariant mass dependent transition form factor for the decays ${\ensuremath{\chi}}_{c1,2}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}J/\ensuremath{\psi}$.

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