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Institute of High Energy Physics, Beijing 100049, People's Republic of China.
G.I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia.
Phys Rev Lett. 2017 Jun 2;118(22):221802. doi: 10.1103/PhysRevLett.118.221802. Epub 2017 May 30.
Using 4.479×10^{8} ψ(3686) events collected with the BESIII detector, we search for the decays ψ(3686)→e^{+}e^{-}χ_{cJ} and χ_{cJ}→e^{+}e^{-}J/ψ, where J=0, 1, 2. The decays ψ(3686)→e^{+}e^{-}χ_{cJ} and χ_{cJ}→e^{+}e^{-}J/ψ are observed for the first time. The measured branching fractions are B(ψ(3686)→e^{+}e^{-}χ_{cJ})=(11.7±2.5±1.0)×10^{-4}, (8.6±0.3±0.6)×10^{-4}, (6.9±0.5±0.6)×10^{-4} for J=0, 1, 2, and B(χ_{cJ}→e^{+}e^{-}J/ψ)=(1.51±0.30±0.13)×10^{-4}, (3.73±0.09±0.25)×10^{-3}, (2.48±0.08±0.16)×10^{-3} for J=0, 1, 2, respectively. The ratios of the branching fractions B(ψ(3686)→e^{+}e^{-}χ_{cJ})/B(ψ(3686)→γχ_{cJ}) and B(χ_{cJ}→e^{+}e^{-}J/ψ)/B(χ_{cJ}→γJ/ψ) are also reported. Also, the α values of helicity angular distributions of the e^{+}e^{-} pair are determined for ψ(3686)→e^{+}e^{-}χ_{c1,2} and χ_{c1,2}→e^{+}e^{-}J/ψ.
利用北京谱仪III（BESIII）探测器收集的4.479×10⁸个ψ(3686)事例，我们寻找衰变过程ψ(3686)→e⁺e⁻χcJ和χcJ→e⁺e⁻J/ψ，其中J = 0、1、2。首次观测到了衰变过程ψ(3686)→e⁺e⁻χcJ和χcJ→e⁺e⁻J/ψ。测得的分支比为：对于J = 0、1、2，B(ψ(3686)→e⁺e⁻χcJ)分别为(11.7±2.5±1.0)×10⁻⁴、(8.6±0.3±0.6)×10⁻⁴、(6.9±0.5±0.6)×10⁻⁴；对于J = 0、1、2，B(χcJ→e⁺e⁻J/ψ)分别为(1.51±0.30±0.13)×10⁻⁴、(3.73±0.09±0.25)×10⁻³、(2.48±0.08±0.16)×10⁻³。还报告了分支比B(ψ(3686)→e⁺e⁻χcJ)/B(ψ(3686)→γχcJ)和B(χcJ→e⁺e⁻J/ψ)/B(χcJ→γJ/ψ)的比值。此外，还确定了ψ(3686)→e⁺e⁻χc1,2和χc1,2→e⁺e⁻J/ψ过程中e⁺e⁻对的螺旋度角分布的α值。
