RESULTS FROM THE L3 EXPERIMENT AT LEP

In this report we summarize the major results from the first three years of running of the L3 detector at the Large Electron Positron collider (LEP). The L3 detector was designed to measure electrons, photons and muons with high precision; it has achieved (DELTAE/E) almost-equal-to 1.4% for electrons and photons at E = 45 GeV and (DELTAp/p) almost-equal-to 2.5% for muons at p = 45 GeV. Most of the experimental results presented are based on approximately 500 000 Z events. The data provide four independent checks of the Standard Model weak neutral currents to an accuracy of almost-equal-to 1%. These are: the measurement of Z parameters; the measurement of the forward-backward charge asymmetry of lepton pairs; the measurement of asymmetry parameters from Z --> bbBAR decays; and the measurement of the tau lepton polarization asymmetry. The data also provide information on weak charged currents from measurements of b hadrons such as decay width, lifetime, and B0-B0BAR mixing, and from measurements Of tau leptons such as their lifetime and branching ratios. The large number of Z events and the resolution of the L3 detector allow precision tests of QED and QCD, including the production of pi0, eta and hard photons. Leptonic final states with hard isolated photons are analyzed and high mass photon pairs are observed. Higgs boson production has not been observed and limits are given in the context of the Standard Model and its supersymmetric extensions. We also present upper limits on rare Z decays such as Z --> gammagammagamma and on flavor violating decays such as Z --> etau, mutau. Finally, upper limits obtained in the search for various new particles and new interactions are reported

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

Search For Nonminimal Higgs Bosons In Z0 Decays

We report on a search for the neutral and charged Higgs bosons predicted by models of spontaneous symmetry breaking with more than one Higgs doublet field. No signals are observed. We set model-independent limits on masses or branching ratios of singly and pair-produced neutral and charged Higgs bosons. In addition, we interpret our results in the framework of a general two-doublet Higgs model and the Minimal Supersymmetric extension of the Standard Model

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

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

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

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

Contains fulltext : 26248.pdf (publisher's version ) (Open Access

A PRECISION EXPERIMENT ON ELECTRONS, PHOTONS AND MUONS AT LHC

We describe the upgrade of the L3 detector for running at LHC. The principle goals are the precise measurement of electrons, photons and muons