QCD studies with e+e- annihilation data at 172-189 GeV

TL;DR

This paper analyzes hadronic events from electron-positron annihilation at energies 172-189 GeV, measuring event shapes, particle multiplicities, and extracting QCD parameters, confirming consistency with previous results at the Z boson mass.

Contribution

It provides new measurements of alpha_s, <nch>, and xi_0 at higher energies, validating QCD predictions and Monte Carlo models against experimental data.

Findings

Measured alpha_s values are consistent with previous determinations.

Event shape distributions are well described by QCD calculations.

Charged particle multiplicity agrees with theoretical expectations.

Abstract

We have studied hadronic events from 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 <nch> 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, <nch> and xi_0 are consistent with previous determinations at sqrt{s}=MZ.