Measurement of the direct photon spectrum inΥ(1S)decays

Abstract
Using data taken with the CLEO II detector at the Cornell Electron Storage Ring, we have determined the ratio of branching fractions: RγΓ(Υ(1S)γgg)/Γ(Υ(1S)ggg)=[2.75±0.04(stat)±0.15(syst)]%. From this ratio, we have determined the QCD scale parameter ΛMS¯ (defined in the modified minimal subtraction scheme) to be ΛMS¯=233±11±59 MeV, from which we determine a value for the strong coupling constant αs(MΥ(1S))=0.163±0.002±0.014, or αs(MZ)=0.110±0.001±0.007.
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