Observation of direct photons in ϒ and ϒ′ decays and determination of the QCD scale parameter

Abstract Using the CUSB detector, we have measured the high energy direct photon spectrum from ϒ and ϒ ′ decays. These photons are assumed to arise from the decays ϒ, ϒ ′ → γ gg. We determine the ration >( gg gg/>(ggg) to be 0.0299 ± 0.0059 for the ϒ and 0.0337 ± 0.0114 for the ϒ ′ . From these results we obtain: α s = 0.226 −0.042 +0.067 , λ MS = 116 −57 +105 MeV for ϒ → γ gg, and α S = 0.197 −0.055 +0.123 , λ MS = 80 −59 +195 MeV for ϒ ′ → gg gg.