Determination of the Strong Coupling Alpha

An experimental determination of the strong coupling alpha_{s}, and Lambda_{overline{MS }}, the fundamental scale parameter of QCD, have been extracted from the differential jet rates of multi-hadronic final states in e^+e^ - annihilations using the AMY detector at TRISTAN. The theoretical predictions from Next-to-Leading-Logarithm (NLL) Parton-Shower QCD calculations are compared to the data. The use of NLL allows one to fix the QCD scale parameter, which significantly reduces the systematic effects associated with the choice of a renormalization scale. The precision of previous extractions of alpha_ {s} based on second-order Matrix Element calculations have been severely limited by renormalization scale uncertainties. Using a NLL calculation we obtain alpha_{s}(M _{rm Z}) = 0.119 +/- 0.006 (total error) and its corresponding Lambda{(5)over MS} is 240 +/- _sp{65 }{80} MeV (total error). Systematic errors due to fragmentation and jet-clustering schemes are discussed. Comparisons are made to values of alpha_{s} derived from other measurements, and the running nature of the strong coupling is demonstrated at different energies by the energy dependence of alpha_{s}.