Charmonium decays to γπ0, γη, and γη′

Using data acquired with the CLEO-c detector at the CESR e + e - collider, we measure branching fractions for J/ψ, ψ(2S), and ψ(3770) decays to γπ 0 γη, and γηʹ. Defining R n ≡ B[ψ(nS)→ γη]/B[ψ(nS) → γηʹ], we obtain R 1 = (21.1 ± 0.9)% and, unexpectedly, an order of magnitude smaller limit, R 2 < 1.8% at 90% C.L. We also use J/ψ→ γηʹ events to determine branching fractions of improved precision for the five most copious ηʹ decay modes.