G. Hughes
Lancaster University
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Physics Letters B | 1988
S. Bethke; B. Naroska; F. Foster; K. Ambrus; F. K. Loebinger; S. L. Cartwright; K. Stephens; K. H. Hellenbrand; R. Marshall; J. von Krogh; M. Minowa; J. A. J. Skard; L. Smolik; H. von der Schmitt; J. Spitzer; M. Zimmer; T. Greenshaw; Roger Barlow; P. Steffen; G. Heinzelmann; J. Heintze; G. Hughes; J. Chrin; J. Hagemann; F. Ould-Saada; M. Kuhlen; A.A. Macbeth; U. Schneekloth; E. Elsen; P.G. Murphy
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.
European Physical Journal A | 1986
W. Bartel; L. Becker; R. Felst; D. Haidt; G. Knies; H. Krehbiel; P. Laurikainen; N. Magnussen; R. Meinke; B. Naroska; J.E. Olsson; D. Schmidt; G. Dietrich; T. Greenshaw; J. Hagemann; G. Heinzelmann; H. Kado; C. Kleinwort; M. Kuhlen; A. Petersen; R. Ramcke; U. Schneekloth; G. Weber; K. Ambrus; S. Bethke; A. Dieckmann; E. Elsen; J. Heintze; K. H. Hellenbrand; S. Komamiya
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.
