H. Akbari

A determination of the properties of the neutral intermediate vector boson Z0

Abstract We report the results of first physics runs of the L3 detector at LEP. Based on 2538 hadron events, we determined the mass m z 0 and the width Γ z 0 of the intermediate vector boson Z 0 to be m z 0 =91.132±0.057 GeV (not including the 46 MeV LEP machine energy uncertainty) and Γ z 0 =2.588±0.137 GeV. We also determined Γ invisible =0.567±0.080 GeV, corresponding to 3.42±0.48 number of neutrino flavors. We also measured the muon pair cross section and determined the branching ratio Γ μμ = Γ h =0.056±0.006. The partial width of Z 0 →e + e − is Γ ee =88±9±7 MeV.

Determination of alpha-s from jet multiplicities measured on the Z0 resonance

Whatever the field, major change implies as much as deep transformation of thinking i.e to put in network new skills in particular, those made available by the availability of new technologies. In this context, only one individual cannot join together all necessary skills. It becomes clear that the goal of space valorization cannot be considered without relational investment between the partners and their accumulated background. The local empowerment concerns a collective phenomenon of acquisition and development of skills rests on an learning way appropriate to the potential of the territory to form or promote. The local mediation sets for objective the creation of relations between pre-existent skills and their transfer between the actors, individuals or groups, private or public. But the capacity of the territory to solve these problems will depend closely on the richness of the network and co-operations which it shelters or it will suggest.

Measurement of the inclusive production of neutral pions and charged particles on the Z0 resonance

Abstract We present a study of the inclusive production of neutral pions and charged particles from 112 000 hadronic Z 0 decays. The measured inclusive momentum distributions can be reproduced by parton shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results to e + e − data between √ s = 9 and 91 GeV, we findfind that the evolution of the spectra with center of mass energy is consistent with the QCD predictions.

Measurements of Z0 --> bb decays and the semileptonic branching ratio BR (b --> l + X)

Abstract We have measured the decay properties of Z 0 → b b from a study of inclusive muon and electron events. The average (e and μ) b-quark semileptonic branching ratio has been determined to be BR (b → l + X) = 0.119 ± 0.003 (stat.) ± 0.006 (syst.), assuming the standard model prediction of Γ bb = 378 ± 3 MeV. From the ratio of the number of dilepton events to single lepton events, we find BR (b → l + X) = 0.113 ± 0.010 (stat.) ± 0.006 (syst.), without assumptions on Λ bb . The partial decay width of the Z 0 into b b has been measured to be Λ bb = 385 ± 7 (stat.) ± 11 (syst.) MeV with an additional 19 MeV error from the uncertainty in BR (b → l + X). The average fractional energy of bottom hadrons in Z 0 → b b events has been determined to be 〈 x E 〉 = 0.686 ± 0.006 (stat.) ± 0.016 (syst.).

Measurement of Z0 decays to hadrons and a precise determination of the number of neutrino species

Abstract We have made a precise measurement of the cross section for e+e−→Z0→hadrons with the L3 detector at LEP, covering the s range from 88.28 to 95.04 GeV. From a fit to the Z0 mass, total width, and the hadronic cross section to be MZ0=91.160 ± 0.024 (experiment) ±0.030(LEP) GeV, ΓZ0=2.539±0.054 GeV, and σh(MZ0)=29.5±0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine Γinvisible=0.548±0.029 GeV, which corresponds to 3.29±0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4σ confidence level.

Measurement of electroweak parameters from hadronic and leptonic decays of the Z 0

AbstractWe have studied the reactionse+e−→hadrons,e+e−, μ+ μ− and τ+ τ−, in the energy range 88.2

Measurement of Z0 ---> b anti-b decay properties

\leqq \sqrt s \leqq 94.2

Search for the neutral Higgs bosons of the minimal supersymmetric standard model from Z0 decays

GeV. A total luminosity of 5.5 pb−1, corresponding to approximately 115000 hadronic and 10000 leptonicZ0 decays, has been recorded with the L3 detector. From a simultaneous fit to all of our measured cross section data, we obtain assuming lepton universality: