W. Lackas

Evidence for gluon bremsstrahlung in e+e− annihilations at high energies

Abstract We report our results on the reactions e+e− → hadrons in the energy range 13 ⩽ Ecm ⩽ 31.6 GeV and compare them with qq jets described in the quark-parton model and with first-order QCD predictions including gluon emission (qqg jets). At high energies the observed features of one-sided jet broadening, sea-gull effect and planar events with a three-jet structure represent a gross violation of the parton model without gluons and find a most natural interpretation if gluon bremsstrahlung is included.

Observation of a Narrow Resonance Formed in e+ e- Annihilation at 9.46-GeV

Abstract An experiment using the PLUTO detector has observed the formation of a narrow, high mass, resonance in e+e− annihilations at the DORIS storage ring. The mass is determined to be 9.46±0.01 GeV which is consistent with that of the Upsilon. The gaussian width σ is observed as 8±1 MeV and is equal to the DORIS energy resolution. This suggests that the resonance is a bound state of a new heavy quark-antiquark pair. An electronic width Γee=1.3±0.4 keV was obtained. In standard theoretical models, this favors a quark charge assignment of 1 3 .

A study of jets in electron positron annihilation into hadrons in the energy range 3.1 to 9.5 GeV

Abstract From an analysis of data taken with the detector PLUTO and the DORIS storage rings we have obtained evidence for jet structure in e + e − annihilation with hadrons. Results for mean sphericity, mean thrust, the angular dependence of the jet axis and for 〈 p t 〉 and 〈 p ∥ 〉 with respect to the jet axis are presented. At 9.4 GeV we also discuss the angular dependence of the charged and neutral deposited energy with respect to the jet axis.

Multiplicity Distributions in e+ e- Annihilations at PETRA Energies

Abstract Measurements of the charged multiplicities for hadron production in e+e− annihilation in the center of mass energy range 9–32 GeV have been made. The average charged multiplicity has an energy dependence much stronger than ln s and similar to that reported for pp collisions. Quantitative differences are observed in the magnitude of both the average multiplicity 〈nch〉 and the dispersion Dch for e+e− and pp interactions at the same center of mass energy. 〈nch〉 and the ratio 〈nch/Dch in e+e− annihilations are significantly larger than in pp collisions and are found to be in overall agreement with QCD predictions. KNO scaling is seen to be satisfied.

First observation of hadron production in e+e− collisions at 13 and 17 GeV CMS energy with the pluto detector at petra: Pluto Collaboration

Abstract First results from the magnetic detector PLUTO at the new e + e − storage ring PETRA are shown. The ratio R of the cross section for hadron production to that for μ-pair production has been measured to be R = 5.0 ± 0.5 at 13 GeV and 4.3 ±0.5 at 17 GeV. Both values have an additional systematic error of 20%. The events show a typical 2-jet structure. The mean transverse momentum approaches a constant value with increasing energy implying a shrinkage of the jet opening angle.

Cross-Sections and Event Topologies in e+ e- Annihilation at 13-GeV and 17-GeV Observed with the PLUTO Detector

Abstract First results from the magnetic detector PLUTO at the new e + e − storage ring PETRA are shown. The ratio R of the cross section for hadron production to that for μ-pair production has been measured to be R = 5.0 ± 0.5 at 13 GeV and 4.3 ±0.5 at 17 GeV. Both values have an additional systematic error of 20%. The events show a typical 2-jet structure. The mean transverse momentum approaches a constant value with increasing energy implying a shrinkage of the jet opening angle.

A study of multi-jet events in e+e− annihilation

Abstract A multi-jet analysis of hadronic final states from e + e − annihilation in the energy range 27 E cm S = 0.15 ± 0.03 (stat. error) ± 0.02 (syst. error). The inferred energy distribution of the most energetic parton is in good agreement with the first-order QCD prediction. A scalar-gluon model is strongly disfavoured. Higher-twist contributions to the three-jet sample are found to be small.

Jet analysis of the ϒ(9.46) decay into charged hadrons

Abstract The direct decay into four and more charged particles of the ϒ(9.46) formed in e+e− collisions is analysed for hadron-jet configurations. The results are compared with the expectations of phase space, a q q two-jet model and a QCD three-gluon decay mechanism. Out of these three models, the three-gluon decay describes best the data.

Measurement and QCD analysis of the photon structure function F2(x, Q2)

Abstract We present a measurement of the hadronic structure function F2γ(x, Q2) of the photon in the Q2 range from 10 to 100 GeV2. Data were taken with the PLUTO detector at the e+e- storage ring PETRA. This measurement and previous PLUTO measurements in the Q2 range of 1.5 to 16 GeV2 are compared with higher order QCD calculations. The structure function is consistent with the predicted log Q2 behaviour when charm contributions are subtracted. The x dependence can be well described for 0.1 Λ MS = 183 + 65/ −40( stat. ) + 46/ −36( sys. ) MeV for the QCD scale parameter.

Pion pair production in photon-photon interactions

The processγγπ+π− has been measured with complete particle identification. Cross-sections are presented from near threshold up to the region of thef(1270). In the mass range 0.5–0.7 GeV, crosssections are lower than the Born term predictions and show no evidence for an ε(600). The two-photon width of thef(1270) is found to be in agreement with previous results.