QCD studies with ${\rm e^+e^-}$ annihilation data at 172-189 GeV

Abstract

We have studied hadronic events from $\mathrm{e^+e^-}$ annihilation data at centre-of-mass energies of $\sqrt{s}=$ 172, 183 and 189 GeV. The total integrated luminosity of the three samples, measured with the OPAL detector, corresponds to 250 pb $^{-1}$ . We present distributions of event shape variables, charged particle multiplicity and momentum, measured separately in the three data samples. From these we extract measurements of the strong coupling $\alpha_s $ , the mean charged particle multiplicity $\langle n_{\mathrm{ch}}\rangle$ and the peak position $\xi_0$ in the $\xi_p=\ln(1/x_p)$ distribution. In general the data are described well by analytic QCD calculations and Monte Carlo models. Our measured values of $\alpha_s $ , $\langle n_{\mathrm{ch}}\rangle$ and $\xi_0$ are consistent with previous determinations at $\sqrt{s}=M_{\mathrm{Z^0}}$ .