MEASUREMENT OF THE BRANCHING FRACTIONS FOR J/ψ → γπ⁰, γη AND γη′ AND STUDY OF η′ → γπ⁺π^- DECAY DYNAMICS

The decay modes J/ψ → γπ0, γη, and γη′ are analyzed using a data sample of 58 million J/ψ decays collected with the BESII detector at the BEPC. The branching fractions are determined to be [Formula: see text], Br(J/ψ → γη) = (11.23 ± 0.89) × 10-4, and Br(J/ψ → γη′) = (5.55 ± 0.44) × 10-3, where the errors are combined statistical and systematic errors. The ratio of partial widths and the singlet-octet pseudoscalar mixing angle of η-η′ system is determined. The η′ → γπ+π- decay dynamics is studied using 22,000 reconstructed J/ψ → γη′ → γγπ+π- events, the π+π- mass spectrum is fitted using different theoretical descriptions. The preliminary results show that only the ρ(770) is not enough to describe the η′ → γπ+π- decay process and a non-ρ(770) contribution is needed.