P. Koehler

Rapid Growth of Charged Particle Multiplicity in High-Energy e+ e- Annihilations

Abstract Hadron production by e + e − annihilation has been studied for c.m. energies W between 13 and 31.6 GeV. As a function of 1n W the charged particle multiplicity grows faster at high energy than at lower energies. This is correlated with a rise in the plateau of the rapidity distribution. The cross section s d σ /d x is found to scale within ±30% for x > 0.2 and 5 ⩽ W ⩽ 31.6 GeV.

Comparison of e+e− annihilation with QCD and determination of the strong coupling constant

We have analyzed 1113 events of the reaction e+e− → hadrons at CM energies of 12 and 30 GeV in order to make a detailed comparison with QCD. Perturbative effects can be well separated from effects depending on the quark and gluon fragmentation parameters to yield a reliable measurement of the coupling constant αS. At 30 GeV, the result is αS = 0.17 ± 0.02 (statistical) ± 0.03 (systematic). QCD model predictions, using the fragmentation parameters determined along with αS, agree with both gross properties of the final states and with detailed features of the three-jet states.

Evidence for a spin-1 gluon in three-jet events

High-energy e+e--annihilation events obtained in the TASSO detector at PETRA have been used to determine the spin of the gluon in the reaction e+e- → qqg. We analysed angular correlations between the three jet axes. While vector gluons are consistent with the data (55% confidence limit), scalar gluons are disfavoured by 3.8 standard deviations, corresponding to a confidence level of about 10-4. Our conclusion is free of possible biases due to uncertainties in the fragmentation process or in determining the qqg kinematics from the observed hadrons.

The Tasso Gas and Aerogel Cherenkov Counters

Abstract We describe the gas and erogel threshold Cherenkov counters built for the TASSO experiment at the DESY e + e − storage ring PETRA. The counters are arranged in two diametrically opposed groups as part of the two hadron arms. The gas counters contain Freon 114 and CO 2 respectively; 128 ellipsoidal mirrors focus the Cherenkov light through funnels onto Philips 5″ photomultipliers coated with wavelength shifter. β = 1 charged particles are detected with at least 99.9% efficiency. The aerogel counters are of the diffusing wall type. They have a sensitive area of 12 m 2 , divided into 32 cells and use a total of 192 RCA Quantacon 5″ photomultipliers. The average aerogel refractive index is around 1.025. The efficiency for β = 1 charged particles is 98%. Design considerations, prototype evaluation, construction details, and performance of the final counter system are described.

Charged pion, kaon, proton and antiproton production in high energy e+e− annihilations

Abstract Production of pions, kaons, protons and antiprotons has been studied in e + e − annihilations at 12 and 30 GeV centre of mass energy using time of flight techniques. The fractional yield of charged kaons and baryons appears to rise with outgoing particle momentum. At our highest energy at least 40% of e + e − annihilations into hadrons are estimated to contain baryons.

Production and properties of the τ-lepton in e+e− annihilation at C.M. energies from 12 to 31.6 GeV

We have observed τ production in e+e− annihilation at centre-of-mass energies between 12 and 31.6 GeV with cross sections in agreement with the QED τ-pair cross section. Branching ratios for τ decay have been measured and are consistent with the world averages. We have determined the cutoff parameters of QED Λ+ (Λ−) to be > 73 GeV (82 GeV) and have obtained an upper limit on the τ lifetime of 1.4 × 10−12 s(95% CL).

Test of QED in e+e− annihilation at energies between 12 and 31.6 GeV

We have measured the reactions e+e− → e+e− → μ+μ− and e+e− → γγ at c.m. energies between 12 and 31.6 GeV. Excellent agreement with the predictions of QED has been found, resulting in cut off parameters Λ+ > 112 GeV and Λ− > 139 GeV for the first process and Λ+ > 34 GeV and Λ− > 42 GeV (95% c.1.) for the last one. A limit on the Weinberg angle of sin2θW < 0.55 (95% c.1.) has been obtained.

Two-photon excitation of the tensor mesonf0(1270)

We have measured charged particle pair production in two-photon scattering at thee+e− storage ring PETRA. While the main source of such events is the production of lepton pairs, the presence of an additional process is clearly indicated by the measured invariant mass distribution of the two particles and their angular distributions. We determine that the excess is mainly due to the decayf0(1270)→π+π-. We derive a width Γ(f0→γγ)=3.2±0.2±0.6 keV (statistical and systematic).

K0 production in e+e− annihilations at 30 GeV center of mass energy

Inclusive K0-production has been measured in e+e- annihilation at a center of mass energy of about W = 30 GeV. The ratio of K0 + K0 production to μ+μ- production is RK0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than RK0 at W = 7 GeV. The cross sections (s/β) dσ/dx is consistent with a scaling behaviour.

E+ e- Annihilation at High-Energies and Search for the t-Quark Continuum Contribution

AbstractMeasurements ofR, sphericity and thrust are presented for c.m. energies between 12 and 31.6 GeV. A possible contribution of at