Search for supersymmetric particles at 130 GeV<root s<140 GeV at LEP

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Inclusive J, Psi' and Chi(c) production in hadronic Z decays

We report on measurements of the inclusive production of J, psi' and chi(c) mesons in hadronic Z decays, based on 3.2 million hadronic events collected using the L3 detector at LEP. The J and psi' mesons are reconstructed through their decays into lepton pairs, while the chi(c) mesons are reconstructed via the decay mode chi(c) --> J + gamma. The measured branching fractions are: Br(Z --> J + X) = (3.40 +/- 0.23 (stat.) +/- 0.27 (sys.)) x 10(-3), Br(Z --> psi' + X) = (1.6 +/- 0.5 (stat.) +/- 0.3 (sys.)) x 10(-3) Br(Z --> chi(cl) + X) = (2.7 +/- 0.6 (stat.) +/- 0.5 (sys.)) x 10(-3). In the absence of a clear chi(c2) signal, the upper limit at 90% C.L. is set: Br(Z --> chi(c2) + X) < 3.2 x 10(-3). (C) 1997 Elsevier Science B.V

Search for neutral Higgs boson production through the process e(+)e(-)->Z(*)H(0)

The results of the searches for neutral Higgs boson production in the process e(+)e(-) --> Z* H-0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z(0) decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doubler Model and limits on the nonstandard Higgs boson production through the process e(+)e(-) --> Z*h(0) are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state

A Measurement of Pi-Polarization at Lep

With a data sample of 86 000 Z --> tau(+)tau>(-)(gamma) events collected in 1990 through 1993 we have measured the polarization of tau-leptons as a function of the production polar angle using the following 1-prong tau decay modes: tau(-) --> e(-)(e) nu(tau),tau(-) --> mu(-)(mu)nu(tau), tau(-) --> pi(-)(K-)nu(tau),tau(-) --> rho(-)nu(tau) and tau(-) --> a(1)(-)nu(tau). We obtain for the ratio of vector to axial-vector weak neutral couplings for electrons gVe/gAe = 0.0791 +/- 0.0099(stat) +/- 0.0025(syst) and taus gV tau/gA tau = 0.0752 +/- 0.0063(stat) +/- 0.0045(syst) consistent with the hypothesis of e - tau universality. Assuming universality of the e - tau neutral current we determine the effective electroweak mixing angle to be sin(2) theta(W)(eff) = 0.2309 +/- 0.0016

Measurement of the B-d(0) meson oscillation frequency

Time-dependent B-d(0)-(B) over bar(d)(0) mixing is studied using 1.5 million hadronic Z decays collected by L3. Semileptonic B decays are selected by requiring at least one reconstructed lepton in both thrust hemispheres. Charge correlations between the tagged leptons are studied as a function of proper time. The proper time of the b-hadron decay is measured by reconstructing the production and decay vertices using a silicon microvertex detector: The measured B-d(0) meson oscillation frequency corresponds to a mass difference Delta m(d) between the two B-d(0) mass eigenstates of Delta m(d) = (0.496(-0.051)(+0.053) (stat) +/- 0.043 (syst)) ps(-1)

A measurement of τ\tau polarization at LEP

With a data sample of 86 000 Z → τ+τ-(γ) events collected in 1990 through 1993 we have measured the polarization of τ-leptons as a function of the production polar angle using the following 1-prong τ decay modes: τ-→e-vevτ, τ-→π- (K-)vτ, τ-→ρ{variant}-vτ and τ-→a1-vτ. We obtain for the ratio vector to axial-vector weak neutral couplings for electrons gVe/gAe=0.0791±0.0099(stat)±0.0025 (syst) and taus gVτ/gAτ=0.0752±0.0063 (stat)±0.0045 (syst) consistent with the hypothesis of e - τ universality. Assuming universality of the e - τ neutral current we determine the effective electroweak mixing angle to be sin2 θeffw = 0.2309 ± 0.0016. © 1994

SEARCH FOR ANOMALOUS PRODUCTION OF SINGLE-PHOTON EVENTS IN E+E- ANNIHILATIONS AT THE Z RESONANCE

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 2Ebeam. No events were found. The results have been interpreted within a composite Z model and a supergravity model with a light gravitino. © 1992

Measurement of inclusive production of neutral hadrons from Z decays

We present a study of the inclusive production of π0, η, Ks0 and Λ based on 929,000 hadronic Z decays recorded with the L3 detector at LEP. The measured inclusive momentum distributions have been compared with predictions from parton shower models as well as an analytical Quantum Chromodynamics calculation. Comparing to low energy e+e- data, we find that QCD describes the energy evolution of the hadron spectrum. © 1994

Measurement of Cross-sections and Leptonic Forward-backward Asymmetries At the Z-pole and Determination of Electroweak Parameters

We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at the Z peak with the L3 detector at LEP. The total luminosity of 40.8 pb-1 collected in the years 1990, 1991 and 1992 corresponds to 1.09 . 10(6) hadronic and 0.98 . 10(5) leptonic Z decays observed. These data allow us to determine the electroweak parameters. From the cross sections we derive the properties of the Z boson: M(Z) = 91 195 +/- 9 MeV GAMMA(Z) = 2494 +/- 10 MeV GAMMA(had) = 1748 +/- 10 MeV GAMMA(l) = 83.49 +/- 0.46 MeV, assuming lepton universality. We obtain an invisible width of GAMMA(inv) = 496.5 +/- 7.9 MeV which, in the Standard Model, corresponds to a number of light neutrino species of N(v) = 2.981 +/- 0.050. Using also the three leptonic forward-backward asymmetries and the average tau polarization, we determine the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons to be: g(V)-l = -0.0378(+0.0045/-0.0042) g(A)-l = -0.4998 +/- 0.0014 Within the framework of the Standard Model, and including our measurements of the Z --> bbBAR forward-backward asymmetry and partial decay width, we derive an effective electroweak mixing angle of sin2 theta(W)BAR = 0.2326 +/- 0.0012. We obtain an estimate for the strong coupling constant, alpha(s) = 0.142 +/- 0.013, and for the top-quark mass, m(t) = 158(+32/-40) +/- 19(Higgs) GeV, where the second error arises due to the uncertainty in the Higgs-boson mass