Tests of power corrections for event shapes in ${\mathrm{e^+e^-}$ annihilation

Abstract.

A study of perturbative QCD calculations combined with power corrections to model hadronisation effects is presented. The QCD predictions are fitted to differential distributions and mean values of event shape observables measured in ${\mathrm{e^+e^-}$ annihilation at centre-of-mass energies from ${\sqrt{s}} =14$ to 189 GeV. We investigate the event shape observables thrust, heavy jet mass, C-parameter, total and wide jet broadening and differential 2-jet rate and observe a good description of the data by the QCD predictions. The strong coupling constant $\alpha_{\mathrm{S}}(M_{\mathrm{Z}^0})$ and the free parameter of the power correction calculations $\alpha_0({\mathrm{2 GeV}})$ are measured to be

\begin{displaymath} \alpha_{\mathrm{Z}}(M_{\mathrm{Z}^0} = 0.1171^{+0.0032}_{-0.0020} \;\;\;\mathrm{and}\;\;\; \alpha_0({\mathrm{2 GeV}}) = 0.513^{+0.066}_{-0.045} \;\;\;. \end{displaymath}

The predicted universality of $\alpha_0$ is confirmed within the uncertainties of the measurements.