G. Alverson

Determination of alpha-S from hadronic event shapes measured on the Z0 resonance

Abstract We present a study of the global event shape variables thrust and heavy jet mass, of energy-energy correlations and of jet multiplicities based on 250 000 hadronic Z 0 decays. The data are compared to new QCD calculations including resummation of leading and next-to-leading logarithms to all orders. We determine the strong coupling constant α s (91.2 GeV) = 0.125±0.003 (exp) ± 0.008 (theor). The first error is the experimental uncertainty. The second error is due to hadronization uncertainties and approximations in the calculations of the higher order corrections.

Isolated Hard Photon-Emission in Hadronic Z0 Decays

Abstract We report on a study of energetic, isolated photons in a sample of ∼ 320 000 Z 0 hadronic decays. Energetic isolated photons probe the short-distance structure of QCD. We compare our data with the prediction of several QCD-based calculations. A search for new processes with one or two photons in the hadronic final state is also presented. No evidence for physics beyond the standard model is found.

A Measurement of Tau Polarization in Z0 Decays

Abstract The polarization of τ leptons produced in e+e− → τ+τ−(γ) is measured using a sample of 8977 τ+τ − pairs collected near the peak of the Z0 resonance. A polarization of −0.132±0.026(stat)±0.021(syst.) is determined. This corresponds to a ratio of the vector to the axial-vector coupling constants of the τ lepton to the weak neutral current of gVτ/gAeffτ = 0.067±0.017. This leads to a value of the effective sin2 θw at the Z0 resonance of sin2 θeff = 0.2326±0.0043.

Inclusive J production in Z 0 decays

Abstract Inclusive J production in Z0 decays is observed via the leptonic decay mode J → l+l− (l = e,μ). We measure the branching ratio Br(Z0 → J + X) = (4.1 ± 0.7 (stat.) ± 0.3 (sys.)) × 10−3. We have calculated the fraction of the J mesons from b-hadron decay and find a branching ratio of Br(b → J + X)= (1.3±0.2(stat.)±0.2(sys.)) × 10−2. We determine the average fractional energy of bottom hadrons 〈XE > = 0.70±0.03 (stat.)+0.02−0.01 (sys.) using the momentum spectrum of the J mesons. From a study of the angle between the J and the most energetic jet, we set an upper limit on the branching ratio Br ( Z 0 → q q g ∗ ; g ∗ → J + X ) −4 at 90% confidence level.

A Test of Quantum Electrodynamics in the Reaction E+E- -]Gamma-Gamma(Gamma)

Abstract We have measured the total and differential cross sections of the reaction e + e − → γγ ( γ ) at center-of-mass energies around 91 GeV, with an integrated luminosity of 14.2 pb −1 . The results are in good agreement with QED predictions. We set lower limits, at 95% confidence level, on the QED cutoff parameters of Λ + > 139 GeV, Λ − > 108 GeV and on the mass of an excited electron of m e∗ > 127 GeV . We searched for Z 0 rare decays with photonic signitures in the final state. Upper limits, at 95% confidence level, for branching ratio of Z 0 decaying into π 0 γ / γγ , νγ and γγγ are 1.2 × 10 −4 , 1.8 × 10 −4 , 3.3 × 10 −5 respectively.

Search for the neutral Higgs boson

Abstract We have searched for the neutral Higgs boson produced in decays of the Z0 through the process e + e − → Z 0 → H 0 Z 0∗ . The data sample analyzed corresponds to 111 200 hadronic decays of the Z0. Combining the results of this analysis with previous L3 results we exclude a minimal standard model Higgs boson in the mass range 0

Search for Anomalous Production of Single-Photon Events in E+E- Annihilations at the Z Resonance

Abstract Using a sample of e+e− annihilation events collected at the Z resonance corresponding to an integrated luminosity of 11.2 pb−1, we have searched for γX final states where X represents stable, weakly interacting particles and the energy of the photon is greater than 1 2 E beam . No events were found. The results have been interpreted within a composite Z model and a supergravity model with a light gravitino.

Measurement of inclusive eta production in hadronic decays of the Z0

Abstract We present a study of the inclusive η production based on 300 000 hadronic Z 0 decays. The measured inclusive momentum distribution can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results with low energy e + e − data, we find that QCD describes both the shape and the energy evolution of the η spectrum. The comparison of η production rates in quark- and gluon-enriched jet samples does not show statistically significant evidence for more abundant production of η mesons in gluon fragmentation.