I. P. Duerdoth

Experimental Investigation of the Energy Dependence of the Strong Coupling Strength

The energy dependence of the relative production rate of three-jet events is studied in hadronic e+e− annihilation events at center of mass energies between 22 and 46.7 GeV. Three-jet events are defined by a jet finding algorithm which is closely related to the definition of resolvable jets used in O(αs2) perturbative QCD calculations, where the relative production rate of three-jet events is roughly proportional to the size of the strong coupling strength. The production rates of three-jet events in the data decrease significantly with increasing centre of mass energy. The experimental rates, which are independent of fragmentation model calculations, can be directly compared to theoretically calculated jet production rates and are in good agreement with the QCD expectations of a running coupling strength. The hypothesis of an energy independent coupling constant can be excluded with a significance of four standard derivations.

Experimental studies on multijet production ine+e− annihilation at PETRA energies

Hadronic jet production bye+e−-annihilation has been studied in the energy range of 14.0–46.7 GeV. The data have been analysed in terms of a cluster algorithm and other topological quantities. The results are compared with 2nd order QCD calculations which incorporate models for the fragmentation of quarks and gluons into hadrons. At the higher energies we observe more spherical and 4-jet like events than predicted by these calculations. We cannot achieve a simultaneous description of the observed 3- and 4-jet production by adjusting the strong coupling constant αs or the fragmentation parameters of the 2nd order QCD models. The observed excess of spherical events can partially be explained by the production of multi-parton events expected from higher order QCD contributions. Consequences of the presented results for the value of αs, determined in previous analyses, are discussed. QCD parton shower models, including soft gluon interference, are able to describe the observed number of spherical events.

Observation of planar three-jet events in e+e− annihilation and evidence for gluon bremsstrahlung

Abstract Topological distributions of charged and neutral hadrons from the reaction e+e− → multihadrons are studied at √s of about 30 GeV. An excess of planar events is observed at a rate which cannot be explained by statistical fluctuations in the standard two-jet process. The planar events, mostly consisting of a slim jet on one side and a broader jet on the other, are shown actually to possess three-jet structure by demonstrating that the broader jet itself consists of two collinear jets in its own rest system. Detailed agreement between data and predictions is obtained if the process e + e − →q q g is taken into account. This strongly suggests gluon bremsstrahlung as the origin of the planar three-jet events. By comparison of the data with the qqg-model we obtain a value for the strong coupling constant of αS(q2 = 0.17 ± 0.04.

Total cross section for hadron production by e+e− annihilation at petra energies

Abstract The cross section for the process e+e− → multihadrons has been measured at the highest PETRA energies. We measure R (the total cross section in units of the point-like e+e- → μ+μ- cross section) to be 2.9 ± 0.7, 4.0 ± 0.5, 4.6 ± 0.4 and 4.2 ± 0.6 at s of 22, 27.7, 30 and 31.6 GeV, respectively. The observed average multiplicity, together with existing low energy data, indicate a rapid increase in multiplicity with increasing energy.

EXPERIMENTAL-STUDY OF JETS IN ELECTRON-POSITRON ANNIHILATION

Abstract Data on hadron production by e + e − -annihilation at c.m. energies between 30 GeV and 36 GeV are presented and compared with two models both based on first-order QCD but using different schemes for the fragmentation of quarks and gluons into hadrons. In one model the fragmentation proceeds along the parton momenta, in the other along the colour-anticolour axes. The data are reproduced better by fragmentation along the colour axes.

Test of Quantum Electrodynamics at {PETRA}

Differential cross sections for the reactions e+e− → e+e− and e+e− → γγ are given for energies between 27.7 and 31.6 GeV. The results agree with the predictions of standard quantum electrodynamics and set lower limits to the usual cut-off parameters of up to 104 GeV. A limit on the Weinberg angle, sin2θW < 0.63, is obtained at unprecedentedly high q2.

A measurement of the electroweak induced charge asymmetry in e+e−→bb̄☆

Abstract The forward-backward charge asymmetry for the process e + e − → b b → μ ± + hadrons has been measured using the JADE detector at PETRA. An asymmetry of (−22.8 ± 6.0 ± 2.5)% was observed at an average center of mass energy of 34.6 GeV. For comparison, an asymmetry of −25.2% is expected on the basis of the standard Glashow-Salam-Weinberg model.

Measurement of resonance production in the reactionsγγ →π0π0 andγγ →π0η

AbstractResonance production in the γγ reactionse+e−→e+e+e−π0π0 ande+e−π0η has been studied with the JADE detector at PETRA. The decay widths into γγ of thef2(1270),a0(980) anda2(1320) were measured to be

BARYON PRODUCTION IN E+E(-)-ANNIHILATION AT PETRA

\Gamma _{\gamma \gamma } (f_2 (1270)) = 3.19 \pm 0.09_{ - 0.38}^{ + 0.22}