Observation of ψ(3686) → e⁺e⁻χ_{cJ} and χ_{cJ} → e⁺e⁻J/ψ

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Abstract

Using 4.479 x 10⁸ 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.

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Keywords

Electron-positron interactions, Electroweak interactions, Mesons, Electrons, Branching fractions (Nuclear physics), Particles (Nuclear physics)—Helicity

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This work is supported in part by National Key Basic Research Program of China under Contract No. 2015CB856700; National Natural Science Foundation of China (NSFC) under Contracts No. 11125525, No. 11235011, No. 11322544, No. 11335008, No. 11425524, No. 11521505, and No. 11575198; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. 11179007, No. U1232201, and No. U1332201; CAS under Contracts No. KJCX2-YW-N29 and No. KJCX2-YW-N45; German Research Foundation DFG under Contracts No. Collaborative Research Center CRC-1044, No. FOR 2359; Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) under Contract No. 530-4CDP03; Ministry of Development of Turkey under Contract No. DPT2006K-120470; Russian Foundation for Basic Research under Contract No. 14-07-91152; U.S. Department of Energy under Contracts No. DE-FG02-05ER41374, No. DE-SC-0010504, No. DE-SC0012069, and No. DESC0010118; U.S. National Science Foundation; WCU Program of National Research Foundation of Korea under Contract No. R32-2008-000-10155-0.

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©2017 American Physical Society.

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