Measurement of branching fractions for ψ ( 3686 ) → γ η ' , γ η , and γ π 0
In this paper, using a data sample of 448 x 10 6 ψ(3686) events collected with the BESIII detector operating at the BEPCII storage ring, the decays ψ(3686) → γη and ψ(3686) → γπ 0 are observed with a statistical significance of 7.3σ and 6.7σ, respectively. The branching fractions are measured to be β(ψ(3686) → γη) = (0.85 ± 0.18 ± 0.05) x 10 -6 and β(ψ(3686) → γπ 0 ) = (0.95 ± 0.16 ± 0.05) x 10 -6 . Finally, in addition, we measure the branching fraction of ψ(3686) → γη' to be β(ψ(3686) → γη') = (125.1 ± 2.2 ± 6.2) x 10 -6 , which represents an improvement of precision over previous results.