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Based on (2712. 4 14. 3) 10^6 e^+e^- (3686) events collected with the BESIII detector operating at the BEPCII collider, we report the first evidence of ₂₀ decays and the first observation of ₂₁, ₂ decays, with significances of 4. 5, 11. 3 and 13. 0, respectively. The decay branching fractions of ₂₀, ₁, ₂ are measured to be (2. 991. 240. 19) 10^-5, (6. 010. 900. 40) 10^-5, and (7. 130. 810. 36) 10^-5, where the first uncertainties are statistical and the second systematic. No obvious enhancement near the production threshold or excited state is found in the (or) system.
Collaboration et al. (Fri,) studied this question.
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