Determination of αs from a measurement of the direct photon spectrum in Γ(1S) decays
1987
Abstract Using the ARGUS detector at the
DORISII e + e −
storage ringwe have measured direct photons from the decay ???(1 S )→ γgg . The ratio R γ = Γ (???(1S)→ γgg )/ Γ (???(1S)→ ggg )=(3.00±0.13±0.18)% has been determined, from which we deduce values of the strong coupling constant α s =0.225±0.011±0.019 and the QCD
scale parameterΛ MS =115±17±28 MeV defined in the modified
minimal-subtraction scheme. The shape of the measured spectrum clearly rules out the predictions of the lowest order QCD calculations.
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