G. Dietrich

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.

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.

Experimental evidence for differences in 〈p⊥〉 between quark jets and gluon jets

Abstract We want to dedicate this work to our friend Peter Dittman who contributed so much to the JADE experiment and who died on 31.8.1982.

PRECISE MEASUREMENT OF TOTAL CROSS SECTIONS FOR THE PROCESS e+e - ~ MULTIHADRONS IN THE CM ENERGY RANGE BETWEEN 12.0 AND 36.4 GeV

The total cross section for the process e+e− → hadrons has been measured in the CM energy range between 12.0 and 36.4 GeV using the JADE detector with a typical systematic error of ±3%. The ratio is found to be constant over this range with an average value of 3.97 ± 0.05 (statistical and point-to-point systematic error) ± 0.10 (normalization error). The data were compared with the standard electro-weak interaction model including QCD corrections.

Charged Particle and Neutral Kaon Production in e+ e- Annihilation at PETRA

The mean charged multiplicity as well as its distribution has been measured as a function of c.m. energy in the reactione+e−→hadrons. Fragmentation models are compared with the data. After applying radiative corrections the mean charged multiplicity is measured to be 8.4±0.3±0.6 at 12 GeV, 13.1±0.3±0.6 at 30 GeV and 13.6±0.3±0.6 at 35 GeV. The ratio of mean charged multiplicity to the dispersion (/Dch) is almost constant in the energy range studied, indicating KNO scaling of the charged multiplicity. The inclusive differential cross sections(dσ/dxp) shows scaling violation in the highxp region (xp>0.15). The absolute value of the scaling violation is consistent with the result of 2nd order QCD calculations. The production of neutral kaons has been investigated by identifying the decayKS0→π+π−. The production probability for a strange quark relative to that of au ord quark in the fragmentation, γs, has been determined to be 0.27±0.03±0.05 averaged over c.m. energies from 12 to 35 GeV. Momentum spectra for neutral kaons are presented and are compared with model predictions.

Measurements of energy correlations ine+e−→hadrons

Energy-energy-correlations (EEC) have been measured with the JADE detector at c.m. energies of 14 GeV, 22 GeV and in the region 29 GeV<Ecm<36 GeV. Corrected results are presented of EEC and their asymmetry, which can be directly compared to theoretical predictions. At 〈Ecm〉=34 GeV a comparison with second order QCD predictions yields good agreement for the string model fragmentation resulting in a value of the strong coupling constant αs=0.165±0.01 (stat.). The independent fragmentation models, which yield values of αs between 0.10 and 0.15 depending on the treatment of energy and momentum conservation and of the gluon splitting, do not provide a satisfactory description of the data over the full angular range.

Particle distribution in 3-jet events produced bye−e−-annihilation

We have studied the distribution of particles within and between jets of 3-jet final states produced in the reactione+e−→hadrons at c.m. energies of 22 GeV and 29–36.4 GeV. The lowest energy jet shows distributions of transverse momenta, particle flow, and energy flow which differ significantly from those of the other two jets and from jets of 2-jet events atEcm=14 GeV. First order QCD calculations with subsequent fragmentation of quarks and gluons into hadrons indicate that the lowest energy jet has the largest probability of originating from a gluon. To reproduce the observed differences in an independent parton fragmentation model, the secondary quarks of a gluon jet have to have higher transverse momenta and lower parallel momenta than those of a quark jet. The particle densities between the jets as well as the correlation of transverse and longitudinal momenta of the particles within the jets favour models with fragmentation along the colour axes.

Test of Fragmentation Models by Comparison with Three Jet Events Produced in e+ e- ---> Hadrons

Abstract The energy flow and particle flow distributions of planar three-jet events produced in e+e−→ hadrons at CM energies between 29.5 and 36.4 GeV have been interpreted in terms of the reactions e+e−→q q g and compared with the distributions calculated from two different fragmentation schemes, one based on independent parton fragmentation, the other one on fragmentation along colour flux lines. The particle density at angles between the two highest energy jets is found to decrease more strongly with increasing transverse mass of the particles than the particle density at angles between any of these jets and the lowest energy jet. The high momentum particles within the two most energetic jets are emitted at larger angles with respect to the lowest energy jet than the average particles. These observations are well reproduced by fragmentation along colour flux lines, but not by independent parton fragmentation.

Measurement of the processese+e−→e+e− ande+e−→γγ at PETRA

AbstractCross sections for the reactionse+e−→e+e− (Bhabha scattering) ande+e−→γγ are measured for center-of-mass (c.m.) energies