Measurement of High-Energy Direct Photons in ψ Decays

The inclusive γ and π⁰ momentum distributions at the ψ have been measured. Using these data and estimates of η production, it is found that (4.1 ±{} 0.8)% of ψ decays contain a direct photon with energy greater than 60% of the beam energy. The expected momentum distribution for direct photons calculated to lowest order in quantum chromodynamics is qualitatively different from that observed in the data.