The inclusive semileptonic branching ratios b —► e u X , uX , r vX and vX have been measured at LEP with a Supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie b Supported by the Hungarian OTKA fund under contract number T 14459 c Supported also by the Comisión Interministerial de Ciencia y Technologia d Also supported by CONICET and Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina e Also supported by Panjab University, Chandigarh-160014, India the L3 detector. The analysis is based on 2-jet hadronic Z decays obtained in the data collected between 1991 and 1992. Three separate event samples are analysed, contain­ ing electrons, muons and large missing energy (neutrinos), respectively. From the electron sample, we measure Br(b —> ez/X) (10.89±0.20=b0.51)% and, from the muon sam­ ple, Br(b —► ¡jl vX ) = (10.82±0.15±0.59)%, where the first error is statistical and the second is systematic. From

The two-photon collision reaction e+e~ e+e~/+/~ has been studied at y/s ~ 91 GeV using the L3 detector at LEP for / = e, (i, r. We have analysed untagged configurations where the two photons are quasi-real. Good agreement is found between our measurements and the ö ( a 4) QED expectation. © 1997 Elsevier Science B.V.

We present a study of the inclusive co and r¡f production based on 3,1 million hadronic Z decays recorded with the L3 detector at LEP during 1991-1994. The production rates per hadronic Z decay have been measured to be 1.17 ± 0.17 co mesons and 0.25 ± 0.04 r)' mesons. The production rates and the differential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the differential cross sections can be described by an analytical quantum chromodynamics calculation.

A search for exclusive decays of B[] and mesons has been performed in the channels ̂ J77, Bj —+ J77, Bj —» J7r° and Bs —► J7t°. The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% confidence level: 3.2 x 10~4 on Br(B^ -► J7r°) and the first experimental limits: Br(B° -+ J77) < 1.2 x 10\ Br(Bs -> J77) < 3.8 x 10“ 3, Br(B° -> h r°) < 1.2 x 10-3 .

We present evidence for soft gluon interference, as required by QCD. This interference is expected to manifest itself in an angular ordering of the gluons radiated within a jet. Using hadronic decays of the Z boson in the L3 detector at LEP, we compare variables sensitive to such an angular ordering, namely the energy-energy correlation asymmetry and the newly introduced particle-particle correlation asymmetry, with the predictions of various parton shower models. Only those models which incorporate the expected interference agree with the data.

New measurements at a centre-of-mass energy root s similar or equal to 183 GeV of the hadronic photon structure function F-2(gamma)(x) in the Q(2) interval, 9 GeV2 less than or equal to Q(2) less than or equal to 30 GeV2, 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 centre-of-mass energy of 91 GeV, the evolution of F-2(gamma) With Q(2) is measured in the Q(2) range from 1.2 GeV2 to 30 GeV2. F-2(gamma) shows a linear growth with ln Q(2); the value of the slope alpha(-1)d F-2(gamma)(Q(2))/dlnQ(2) is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Two-photon formation of the charmonium resonance chi(c2), has been studied with the L3 detector at LEP. The chi(c2) is identified through its decay chi(c2) --> gamma J/psi, with a subsequent decay J/psi --> e(+)e(-) or J/psi --> mu(+)mu(-). With an integrated luminosity of 140 pb(-1) at root s similar or equal to 91 GeV and 52 pb(-1) at root s similar or equal to 183 GeV, we measure the two-photon width of the chi(c2) to be Gamma(gamma gamma)(chi(c2)) = 1.02 +/- 0.40 (stat.) +/- 0.15 (sys.) +/- 0.09(BR.) keV. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

The time-integrated B-0(B) over bar(0) mixing parameter and the forward-backward charge asymmetry in the process e(+)e(-) --> b (b) over bar are measured in hadronic Z events containing prompt muons or electrons, collected by the L3 experiment in the years 1990 to 1995. The total sample of 3.3 milion hadronic Z events with a mean centre-of-mass energy of 91.26 GeV yields: A(FB)(b) = 0.0960 +/- 0.0066(stat.) +/- 0.0033(sys.), chi(b) = 0.1192 +/- 0.0068(stat.)+/- 0.0051(sys.). This asymmetry measurement together with measurements at energies away from the Z pole energy yield a pole asymmetry and corresponding effective electroweak mixing angle of: A(FB)(0,b) = 0.1015 +/- 0.0064(stat.) +/- 0.0035(sys.), sin(theta)(2)W<(theta)over bar> = 0.2318 +/- 0.0013. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies from 130 to 183 GeV, corresponding to an integrated luminosity of 88.3 pb(-1). The Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed candidates are consistent with the expectations from Standard Model background processes. A lower limit of 57.5 GeV on the charged Higgs mass is derived at 95% CL, independent of the decay branching ratio Br(H+/- --> tau nu). (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Searches for scalar top and scalar bottom quarks have been performed at center-of-mass energies between 161 GeV and 183 GeV using the L3 detector at LEP. No signal is observed. Model-independent limits on production cross sections are determined for the two decay channels (t) over tilde --> c<(chi)over tilde>(0)(1) and (b) over tilde(1) --> b<(chi)over tilde>(0)(1). Within the framework of the Minimal Supersymmetric extension of the Standard Model mass limits are derived. For mass differences between (t) over tilde(1) and <(chi)over tilde>(0)(1) greater than 10 GeV a 95% C.L. limit of 81.5 GeV is set on the mass of the Supersymmetric partner of the left-handed top. A supersymmetric partner of the left-handed bottom with a mass below 80 GeV is excluded at 95% C.L. if the mass difference between bl and <(chi)over tilde>(0)(1) is greater than 20 GeV. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Using the data collected with the L3 detector at LEP between 1990 and 1995, corresponding to an integrated luminosity of 149 pb(-1), the tau longitudinal polarisation has been measured as a function of the production polar angle using the tau decays tau(-) --> h(-)nu(tau) (h = pi,rho,a(1)) and tau(-)-->l(-)<(nu)over bar>(l)nu(tau) (l = e,mu). From this measurement the quantities A(c) and A(tau), which depend on the couplings of the electron and the tau to the Z, are determined to be A(c) = 0.1678 +/- 0.0127 +/- 0.0030 and A(tau) = 0.1476 +/- 0.0088 +/- 0.0062, consistent with the hypothesis of e-tau universality, Under this assumption a value of A(l) = 0.1540 +/- 0.0074 +/- 0.0044 is obtained, yielding the value of the effective weak mixing angle sin(2)<(theta)over bar>(W) = 0.2306 +/- 0.0011. (C) 1998 Elsevier Science B.V. All rights reserved.

The reactions e(+)e(-) --> e(+)e(-)e(+)e(-) and e(+)e(-) --> e(+)e(-)mu(+)mu(-), in a single tag configuration, are studied at LEP with the L3 detector. The data set corresponds to an integrated luminosity of 93.7 pb(-1) at root s = 91 GeV. Differential cross sections are measured for 1.4 GeV2 less than or equal to Q(2) less than or equal to 7.6 GeV2. The leptonic photon structure function F-2(gamma) and azimuthal correlations are measured for e(+)e(-) --> e(+)e(-)mu(+)mu(-). The related structure functions F-A(gamma) and F-B(gamma), which originate from interference terms of the scattering amplitudes, are determined for the first time. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

We analyse e(+)e(-) --> tau tau gamma events using 100 pb(-1) 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(tau) = 0.004 +/- 0.027 +/- 0.023;d(tau) = (0.0 +/- 1.5 +/- 1.3) x 10(16) e.cm.This is a direct measurement of these tau form factors at q(2) = 0. (C) 1998 Elsevier Science B.V. All rights reserved.

Time-dependent B-0-(B) over bar(0) mixing is studied using about two million hadronic Z decays registered by L3 in 1994 and 1995. For this study three techniques are used. Tagging of the b-quark charge at decay time is performed by identifying leptons from semileptonic B decays. The flavour of the b quark at production time is determined from the charge of the lepton in the opposite hemisphere or by using a jet-charge technique. The proper time of the B-particle decay is obtained by reconstructing the production and decay vertices or by a measurement of the lepton impact parameter. The combined result for the frequency of B-d(0) meson oscillations isDelta m(d) = 0.444 +/- 0.040 ps(-1).

We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at a centre-of-mass energy of 183 GeV. The data sample corresponds to an integrated luminosity of 55.3 pb(-1). The distributions of event shape variables and the energy dependence of their mean values are measured. From a comparison with resummed O(alpha(s)(2)) QCD calculations, we determine the strong coupling constant alpha(s) (183 GeV) = 0.1086 +/- 0.0026(exp) +/- 0.0054(th). The charged particle multiplicity distribution and momentum spectrum are studied and the energy dependence of the peak position of the xi(= - ln x(p)) distribution is compared with lower energy measurements and QCD expectations. (C) 1998 Elsevier Science B.V.

Events characterised by large hadronic energy and transverse momentum are selected from the data collected by the L3 detector at LEP at centre-of-mass energies between 161 and 172 GeV, corresponding to an integrated luminosity of 21 pb(-1) The visible mass and the missing mass distributions of the selected events are consistent with those expected from Standard Model processes. This result is combined with that from data taken at the Z resonance to sci an upper limit on the production rate and decay into invisible final states of a non-minimal Higgs boson. as a function of the Higgs mass. Assuming the non-minimal Higgs production cross section to be the same as for the Standard Model Higgs boson and the decay branching fraction into invisible final states to be 100%, a Higgs mass lower limit of 69.6 GeV is derived at 95% confidence level. (C) 1998 Elsevier Science B.V.

An upper limit on the lifetime difference of short- and long-lived B-s(0) masons has been obtained using an inclusive bottom hadron sample from 2 million hadronic Z decays collected by the L3 experiment at LEP. A lifetime fit has been performed on data samples separately enriched in neutral and charged b hadrons. An experimental upper limit on the decay rate difference of short- and long-lived B-s(0) masons of (\Delta Gamma\/Gamma)(Bs0) < 0.67 (95% C.L.) has been determined. In addition, the lifetimes of B + and B-d(0) mesons have been measured to be tau(B+) = 1.66 +/- 0.06 +/- 0.03 ps and tau(B-d(0)) = 1.52 +/- 0.06 +/- 0.04 ps, where the first errors are statistical and the second are systematic. (C) 1998 Elsevier Science B.V. All rights reserved.

Time-dependent B-B̄ mixing is studied using about two million hadronic Z decays registered by L3 in 1994 and 1995. For this study three techniques are used. Tagging of the b-quark charge at decay time is performed by identifying leptons from semileptonic B decays. The flavour of the b quark at production time is determined from the charge of the lepton in the opposite hemisphere or by using a jet-charge technique. The proper time of the B-particle decay is obtained by reconstructing the production and decay vertices or by a measurement of the lepton impact parameter. The combined result for the frequency of Bd meson oscillations is ∆md = 0.444 ± 0.040 ps−1. The L3 Collaboration: Measurement of the Bd − B̄d oscillation frequency 197

A measurement of the inclusive charmless semileptonic branching fraction of beauty hadrons, b --> X-u l nu, has been performed using almost two million hadronic Z decays collected by the L3 experiment at LEP, yielding the result: Br(b --> X-u l nu) = (3.3 +/- 1.0 +/- 1.7) x 10(-3). The first uncertainty is statistical and the second is systematic. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element V-ub extracted from this measurement is: \V-ub\ = (6.0(-1.0-1.9)(+0.8+1.4) +/- 0.2) x 10(-3), where the uncertainties are statistical, systematic and theoretical, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.