Measurement of strong coupling constant from transverse momentum

Data from e+e– annihilation into hadrons at the center of mass energy of 60 GeV are used to study the distribution of momentum components with respect to the jet axis. At high energies, the gluon emission that leads to three jet structures represents a gross violation of the parton model without gluons and finds a most natural interpretation if gluon bremsstrahlung is included. The coupling constant, αs, is measured by two different methods, first by employing the jet clustering algorithm introduced by the JADE group. Using this method, the strong coupling constant is found to be 0.123 ± 0.004. Next, from the event shape distributions, we extract the strong coupling constant, αs, and test its evaluation with energy scale. The results are consistent with the running of αs, expected from QCD predictions. Averaging over different observables, the value of αs is determined to be 0.121 ± 0.007.