S. L. Lloyd

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.

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).

High pT hadron production in photon-photon collisions

We have studied the properties of hadron production in photon-photon scattering with tagged photons at the e+e− storage ring PETRA. A tail in the pT distribution of particles consistent with pT−4 has been observed. We show that this tail cannot be due to the hadronic part of the photon. Selected events with high pT particles are found to be consistent with a two-jet structure as expected from a point-like coupling of the photons to quarks. The lowest-order cross section predicted for γγ → qq, σ = 3 Σ eq4 · σγγ → μμ, is approached from above by the data at large transverse momenta.

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.

Energy scan for narrow states in e+e- annihilation at C.M. energies between 29.90 and 31.46 GeV

A fine energy scan has been performed to search for narrow states in e+e− annihilation at c.m. energies between 29.90 and 31.46 GeV. No such state has been observed. The 90% confidence upper limit on the leptonic decay width times the hadronic decay branching ratio is ΓeeBh<1.6 keV.

A measurement of theD 0 lifetime

We have determined theD0 lifetime from reconstructed vertices ofD0 mesons produced ine+e− annihilations at an average center of mass energy of 42.2 GeV. From fifteen events theD0 lifetime was determined to be (4.3−1.4+2.0±0.8)×10−13s.

Two photon results from TASSO

Two photon annihilation processes were observed with the TASSO detector at the e+e- storage ring PETRA. We report on the analyses of untagged and single tag events.