H. Ackermann

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.

Lepton and hadron pair production in two-photon reactions

Abstract We have measured the production of charged particle pairs in e + e − initiated two-photon reactions. The observed rates and invariant mass spectra agree with expectations from QED if a resonant π + π − production at the f 0 mass is added. Assuming dominance of the helicity 2 production we obtain the width Γ (f 0 → γγ ) = 2.3 ± 0.5 keV.

First measurement of the photon structure function F2

Abstract Using data taken at PETRA we present results on deep inelastic electron photon scattering at momentum transfers 1 Q 2 2 . The results are expressed in terms of the photon structure function F 2 and are compared with QCD predictions and “hadronic” models of the photon. The pointlike component of the photon is found to be dominant.

Energy-energy correlations in e+e− annihilation into hadrons

Abstract Measurements of energy-energy correlations in hadronic final states produced in e + e − annihilation at c.m. energies between 7.7 and 31.6 GeV are presented. The data are compared to perturbative QCD predictions. Good qualitative agreement above 20 GeV c.m. energy is found. The importance of non-perturbative effects is discussed, as well as the detailed behaviour of the correlation near 180°.

Measurement of the reaction e+e− → γγ at CMS energies from 9.4 to 31.6 GeV

Abstract The differential cross section for the reaction e + e − → γγ has been measured in the CMS energy range between 9.4 and 31.6 GeV. The results are found to be in agreement with the predictions of quantum electrodynamics up to momentum transfers- q 2 of 900 GeV 2 . The data set lower limits of about 40 GeV on QED cut-off parameters. We have searched for the decay υ (9.46) → γγ and obtain an upper limit Γ ( υ → γγ )/ Γ ( υ → all)

Two-particle correlations in e+e− annihilation

Abstract We present measurements of two-particle angular correlations in hadron jets produced in e + e − annihilation between 7.7 and 31.6 GeV c.m. energy. The data are compared to predictions of high order perturbative QCD calculations.

Search for a “top” threshold in hadronic e+e− annihilation at energies between 22 and 31.6 GeV

Results on e+e− annihilation into hadrons at c.m. energies between 22 and 31.6 GeV are presented. The data were accumulated with the PLUTO detector at PETRA. The events are dominantly of the two-jet type. The value of the relative hadronic cross section R=3.88 ± 0.22 along with the details of the sphericity and thrust distribution rule out an open (tt) channel (Qt = 23) below 30 GeV. The inclusive muon results support the above conclusion.