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0370-2693r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.Ž . PII: S 0 3 7 0 -2 6 9 3 9 8 0 0 7 3 6 -9 ( ) M. Acciarri et al.r Physics Letters B 434 1998 169- AbstractWe analyse e q e y ™ ttg events using 100 pb y1 of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively: a s 0.004 " 0.027 " 0.023; t d s 0.0 " 1.5 " 1.3 = 10 y16 e P cm. Ž .t This is a direct measurement of these t form factors at q 2 s 0. q 1998 Elsevier Science B.V. All rights reserved.

A search for heavy neutrinos that are isosinglets under the standard SU(2)L gauge group is made at center-of-mass energies 130 -'s -189 GeV with the L3 detector at LEP. Such heavy neutrinos are expected in many extensions of the Standard Model. The search is performed for the first generation heavy singlet neutrino, Ne, through the decay modeNe ™ e + W. We set upper limits on the mixing parameter between the heavy and light neutrino for the heavy neutrino mass range from 80 GeV to 185 GeV.

We present a measurement of the average b-hadron lifetime b at the e

New measurements at a centre-of-mass energy √ s 183 GeV of the hadronic photon structure function F γ 2 (x) in the Q 2 interval, 9 GeV 2 ≤ Q 2 ≤ 30 GeV 2 , are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb −1. Combining with the data taken at a centreof-mass energy of 91 GeV, the evolution of F γ 2 with Q 2 is measured in the Q 2 range from 1.2 GeV 2 to 30 GeV 2. F γ 2 shows a linear growth with ln Q 2 ; the value of the slope α −1 dF γ 2 (Q 2)/d ln Q 2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted.

The three different helicity states of W bosons produced in the reaction e+e-→lvqq at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies √s=183–209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218±0.027±0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation

A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed on data collected at LEP by the L3 detector at center-of-mass energies 130 GeV ≤ p s ≤ 183 GeV. No significant excess of events is observed. Limits on the masses of the lightest neutral and pseudoscalar Higgs bosons are given as a function of tan β. Lower mass limits at the 95% confidence level are set at m h > 70.7 GeV and m A > 71.0 GeV.

We analyse the process τ − → ντ π − π 0 allowing for anomalous weak charged current magnetic and electric dipole moment interactions and determine the effects on the differential and total decay rates. Using recent experimental data we determine the following values for the anomalous magnetic and electric dipole moment parameters, respectively: