D0 Run IIB Upgrade Technical Design Report

title: Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays
abstract: We have measured the probability, $\overline{n}_{\rm{g} \rightarrow c\overline{c}}$, 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 $\overline{n}_{\rm{g} \rightarrow c\overline{c} } = [2.45 \pm 0.29 \pm

title: Higgs candidates in $e^{+} e^{-}$ interactions at $\sqrt{s}$ = 206.6-GeV
abstract: In a search for the Standard Model Higgs boson, carried out on 212.5 pb −1 of data collected by the L3 detector at the highest LEP centre-of-mass energies, including 116.5 pb −1 above s =206  GeV, an excess of candidates for the process e + e − → Z ∗ → HZ is found for Higgs masses near 114.5 GeV. We present an analysis of our data and the characteristics of our strongest candidates.

title: Measurement of the tau branching fractions into leptons
abstract: 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).

title: Measurement of Inclusive Charm Production in Two -Photon Collisions at LEP.
abstract: The cross section of inclusive charm production in two-photon collisions  e+e_ccX) is measured at the Large Electron Positron (LEP) col­ lider at the European Center for Nuclear and Particle Physics (CERN). The data was obtained with the L3 detector at the center-of-mass energy of 91 GeV (LEP1) and for the first time at the center-of-mass energies from 130183 GeV (LEP2). Charmed hadrons are identified by electrons and muons from semileptonic decays. The measured cross section agrees with ne^t-toleading order (NLO) QCD calculations. The direct process 7 7 —► cc is found to be insufficient to describe the data. The measured cross section values and event distributions require contributions from resolved processes, which are sensitive to the gluon density in the photon.

title: Measurement of an elongation of the pion source in Z decays
abstract: We measure Bose-Einstein correlations between like-sign charged pion pairs in hadronic Z~decays with the L3 detector at LEP. The analysis is performed in three dimensions in the longitudinal center-of-mass system. The pion source is found to be elongated along the thrust axis with a ratio of transverse to longitudinal radius of $0.81\pm 0.02 ^{+0.03}_{-0.19}$.

title: Parity-Time Symmetry Breaking beyond One Dimension: The Role of Degeneracy
abstract: We consider the role of degeneracy in Parity-Time (PT) symmetry breaking for non-hermitian wave equations beyond one dimension. We show that if the spectrum is degenerate in the absence of T-breaking, and T is broken in a generic manner (without preserving other discrete symmetries), then the standard PT-symmetry breaking transition does not occur, meaning that the spectrum is complex even for infinitesimal strength of gain and loss. However the realness of the entire spectrum can be preserved over a finite interval if additional discrete symmetries X are imposed when T is broken, if X decouple all degenerate modes. When this is true only for a subset of the degenerate spectrum, there can be a partial PT transition in which this subset remains real over a finite interval of T-breaking. If the spectrum has odd-degeneracy, a fraction of the degenerate spectrum can remain in the symmetric phase even without imposing additional discrete symmetries, and they are analogous to dark states in atomic physics. These results are illustrated by the example of different T-breaking perturbations of a uniform dielectric disk and sphere, and a group theoretical analysis is given in the disk case. Finally, we show that multimode coupling is capable of restoring the T-symmetric phase at finite T-breaking. We also analyze these questions when the parity operator is replaced by another spatial symmetry operator and find that the behavior can be qualitatively different.

title: Ground-state magnetization for interacting fermions in a disordered potential: Kinetic energy, exchange interaction, and off-diagonal fluctuations
abstract: We study a model of interacting fermions in a disordered potential, which is assumed to generate uniformly fluctuating interaction matrix elements. We show that the ground state magnetization is systematically decreased by off-diagonal fluctuations of the interaction matrix elements. This effect is neglected in the Stoner picture of itinerant ferromagnetism in which the ground-state magnetization is simply determined by the balance between ferromagnetic exchange and kinetic energy, and increasing the interaction strength always favors ferromagnetism. The physical origin of the demagnetizing effect of interaction fluctuations is the larger number of final states available for interaction-induced scattering in the lower spin sectors of the Hilbert space. We analyze the energetic role played by these fluctuations in the limits of small and large interaction $U$. In the small $U$ limit we do second-order perturbation theory and identify explicitly transitions which are allowed for minimal spin and forbidden for higher spin. These transitions then on average lower the energy of the minimal spin ground state with respect to higher spin. For large interactions $U$ we amplify on our earlier work [Ph. Jacquod and A.D. Stone,  (2000)] which showed that minimal spin is favored due to a larger broadening of the many-body density of states in the low-spin sectors. Numerical results are presented in both limits.