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Using $4.48 \times 10^{8}$ $\psi(3686)$ events collected with the BESIIIdetector, we search for the decays $\chi_{cJ} \rightarrow \mu^{+}\mu^{-}J/\psi$through the radiative decays $\psi(3686) \rightarrow \gamma\chi_{cJ}$, where$J=0,1,2$. The decays $\chi_{c1,2} \rightarrow \mu^{+}\mu^{-}J/\psi$ areobserved, and the corresponding branching fractions are measured to be$\mathcal{B}(\chi_{c1} \rightarrow \mu^{+}\mu^{-}J/\psi) = (2.51 \pm 0.18 \pm0.20)\times10^{-4}$ and $\mathcal{B}(\chi_{c2} \rightarrow\mu^{+}\mu^{-}J/\psi) = (2.33 \pm 0.18 \pm 0.29)\times10^{-4}$, where the firstuncertainty is statistical and the second one systematic. No significant$\chi_{c0} \rightarrow \mu^{+}\mu^{-}J/\psi$ decay is observed, and the upperlimit on the branching fraction is determined to be $2.0\times10^{-5}$ at 90%confidence level. Also, we present a study of di-muon invariant mass dependenttransition form factor for the decays $\chi_{c1,2} \rightarrow\mu^{+}\mu^{-}J/\psi$.

Study of electromagnetic Dalitz decays $\chi_{cJ} \rightarrow \mu^{+}\mu^{-}J/\psi$