Complexities of atomic structure at CdO/MgO and CdO/Al2O3 interfaces

We report the interface structures of CdO thin films on (001)-MgO and (0001)-Al2O3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO∥(001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO (<3 nm). On the c-Al2O3 substrate, we find that CdO grows with a surface normal of [025]. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides

Charging Effects and Quantum Crossover in Granular Superconductors

The effects of the charging energy in the superconducting transition of granular materials or Josephson junction arrays is investigated using a pseudospin one model. Within a mean-field renormalization-group approach, we obtain the phase diagram as a function of temperature and charging energy. In contrast to early treatments, we find no sign of a reentrant transition in agreement with more recent studies. A crossover line is identified in the non-superconducting side of the phase diagram and along which we expect to observe anomalies in the transport and thermodynamic properties. We also study a charge ordering phase, which can appear for large nearest neighbor Coulomb interaction, and show that it leads to first-order transitions at low temperatures. We argue that, in the presence of charge ordering, a non monotonic behavior with decreasing temperature is possible with a maximum in the resistance just before entering the superconducting phase.Comment: 15 pages plus 4 fig. appended, Revtex, INPE/LAS-00

Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV

A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed using 176.4 pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of 189 GeV. No signal is observed, and the data are consistent with the expected Standard Model background. Lower limits on the masses of the lightest neutral scalar and pseudoscalar Higgs bosons are given as a function of tan(beta). Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h > 77.1 GeV and m_A > 77.1 GeV

Measurement of the Lifetime of the Tau Lepton

The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result with the muon lifetime supports lepton universality of the weak charged current at the level of six per mille. Assuming lepton universality, the value of the strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/- 0.015(exp.) +/- 0.014 (theory)

Search for Extra Dimensions in Boson and Fermion Pair Production in e+e- Interactions at LEP

Extra spatial dimensions are proposed by recent theories that postulate the scale of gravity to be of the same order as the electroweak scale. A sizeable interaction between gravitons and Standard Model particles is then predicted. Effects of these new interactions in boson and fermion pair production are searched for in the data sample collected at centre-of-mass energies above the Z pole by the L3 detector at LEP. In addition, the direct production of a graviton associated with a Z boson is investigated. No statistically significant hints for the existence of these effects are found and lower limits in excess of 1 TeV are derived on the scale of this new theory of gravity

Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays

We have measured the probability, n(g->cc~), of a gluon splitting into a charm-quark pair using 1.7 million hadronic Z decays collected by the L3 detector. Two independent methods have been applied to events with a three-jet topology. One method relies on tagging charmed hadrons by identifying a lepton in the lowest energy jet. The other method uses a neural network based on global event shape parameters. Combining both methods, we measure n(g->cc~)= [2.45 +/- 0.29 +/- 0.53]%

Measurement of the Photon Structure Function at High Q^2 at LEP

The structure functions of real and virtual photons are derived from cross section measurements of the reaction e^+e^ -> e^+e^- + hadrons at LEP. The reaction is studied at \sqrt{s} ~ 91 GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q^2 values between 40 GeV^2 and 500 GeV^2. The other final state electron is either undetected or it is detected at a four-momentum transfer squared P^2 between 1 GeV^2 and 8 GeV^2. These measurements are compared with predictions of the Quark Parton Model and other QCD based models

Measurement of Triple-Gauge-Boson Couplings of the W Boson at LEP

We report on measurements of the triple-gauge-boson couplings of the W boson in e+e- collisions with the L3 detector at LEP. W-pair, single-W and single-photon events are analysed in a data sample corresponding to a total luminosity of 76.7 pb^{-1} collected at centre-of-mass energies between 161 GeV and 183 GeV. CP-conserving as well as both C- and P-conserving triple-gauge-boson couplings are determined. The results, in good agreement with the Standard-Model expectations, confirm the existence of the self coupling among the electroweak gauge bosons and constrain its structure

Measurement of Hadron and Lepton-Pair Production at 130GeV < \sqrt{s} < 189 GeV at LEP

We report on measurements of e+e- annihilation into hadrons and lepton pairs. The data have been collected with the L3 detector at LEP at centre-of-mass energies between 130 and 189 GeV. Using a total integrated luminosity of 243.7 pb^-1, 25864 hadronic and 8573 lepton-pair events are selected for the measurement of cross sections and leptonic forward-backward asymmetries. The results are in good agreement with Standard Model predictions

Measurement of the Tau Branching Fractions into Leptons

Using data collected with the L3 detector near the Z resonance, corresponding to an integrated luminosity of 150pb-1, the branching fractions of the tau lepton into electron and muon are measured to be B(tau->e nu nu) = (17.806 +- 0.104 (stat.) +- 0.076 (syst.)) %, B(tau->mu nu nu) = (17.342 +- 0.110 (stat.) +- 0.067 (syst.)) %. From these results the ratio of the charged current coupling constants of the muon and the electron is determined to be g_mu/g_e = 1.0007 +- 0.0051. Assuming electron-muon universality, the Fermi constant is measured in tau lepton decays as G_F = (1.1616 +- 0.0058) 10^{-5} GeV^{-2}. Furthermore, the coupling constant of the strong interaction at the tau mass scale is obtained as alpha_s(m_tau^2) = 0.322 +- 0.009 (exp.) +- 0.015 (theory)