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Using data taken with the CLEO III detector at the Cornell Electron StorageRing, we have investigated the direct photon spectrum in the decays Upsilon(1S)-> gggamma, Upsilon(2S) -> gggamma, Upsilon}(3S) -> gggamma. The latter two ofthese are first measurements. Our analysis procedures differ from previous onesin the following ways: a) background estimates (primarily from pi^0 decays arebased on isospin symmetry rather than a determination of the pi^0 spectrum,which permits measurement of the Upsilon(2S) and Upsilon(3S) direct photonspectra without explicit corrections for pi^0 backgrounds from, e.g., chi_bJstates, b) we estimate the branching fractions with a parametrized functionalform (exponential) used for the background, c) we use the high-statisticssample of Upsilon(2S) -> pi+ pi- Upsilon(1S) to obtain a tagged-sample ofUpsilon(1S) -> gamma + X events, for which there are no QED backgrounds. Wedetermine values for the ratio of the inclusive direct photon decay rate tothat of the dominant three-gluon decay Upsilon -> ggg(R_gamma=B(gggamma)/B(ggg)) to be: R_gamma(1S)=(2.70+/-0.01+/-0.13+/-0.24)%,R_gamma(2S)=(3.18+/-0.04+/-0.22+/-0.41)%, andR_gamma(3S)=(2.72+/-0.06+/-0.32+/-0.37)%, where the errors shown arestatistical, systematic, and theoretical model-dependent, respectively. Given avalue of Q^2, one can estimate a value for the strong coupling constantalpha_s(Q^2) from R_gamma.

physical review. d. particles, fields, gravitation, and cosmology/physical review. d, particles, fields, gravitation, and cosmology

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Measurement of the direct photon momentum spectrum inΥ(1S),Υ(2S)