No description available.

No description available.

No description available.

No description available.

No description available.

The luminosity system is an integral part of the DO detector that must be properly maintained to provide accurate luminosity measurements for physics analysis. After the addition of a readout layer to the silicon vertex detector in 2006, it was necessary to re-calculate the effective inelastic cross section to which the luminosity monitor is sensitive. The preliminary analysis showed that the luminosity constant did not change with the addition of the extra layer of silicon. A full study of the revised luminosity constant including a complete analysis of systematic uncertainties has been completed. The luminosity constant was determined to be sigmaeff = 48.3 +/- 1.9 +/- 0.6 mb, which reduces the DO contribution to the luminosity measurement uncertainty by almost 3%.

We report the result of a search for the pair production of the light supersymmetric partner of the top quark (t˜1) in 5.4+/-0.3 fb-1 of data from the DO detector at a pp¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino ( n&d5; ), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected and new exclusion limits at the 95% C.L. are set for a portion of the ( mt&d5;1,m n&d5; ) mass plane.

Charged particle tracking and identification are important elements of any elementary particle physics experiment. Transition radiation is often used to separate electrons from heavier charged particles. This thesis describes a combined tracking and transition radiation detector well suited to the high rate environment of the Superconducting Super Collider (SSC). In the proposed "Electrons Muons Partons with Air Core Toroids" (EMPACT) detector at the SSC the straw tubes with 4 mm diameter filled with 50-50 Xenon-CO₂ and polyethylene radiation foams are selected for the tracking system. The principles of operation of proportional chambers have been studied. The size of the tube is related to the characteristics of the filling gas and the desired occupancy.

While we may know the overall quantum numbers of a given meson state and that such a state is necessarily a color singlet, we do not know a priori the relative spin and color alignments of the constituents: the quarks, antiquarks, and gluons. The overall meson wavefunction may have contributions from different spin-color configurations: one where the quark and antiquark alone account for the spin of the meson; or another where a gluon excitation also contributes to the total spin (a hybrid state), while helping to form the color singlet. The determination of the relative contributions of each these configurations to the overall meson state is the focus of this work. We use the lattice formulation of quantum chromodynamics (QCD) and we restrict our analysis to the limit of heavy quark masses. We are therefore able to use a non-relativistic approximation for the quark and antiquark Hamiltonians (NRQCD). This provides the additional separation of the spin- and orbital-angular-momentum degrees of freedom of the quarks. We therefore have a clear separation of basis states where the meson spin is carried by only the quark and antiquark spins, their relative orbital motion, or a combination of the two; and also the state where a gluon excitation is needed, along with the quark and antiquark, to form the correct quantum numbers. Using only the static and kinetic terms of the heavy-quark Hamiltonian we create meson-like correlators with the same quantum numbers, but with different color-spin configurations. From these correlators we extract the masses and amplitudes which form the basis of a two-state system. We then apply the lowest-order spin-dependent interaction at various intermediate time slices to form correlators between different configurations. From these "mixed" correlators we extract the off-diagonal matrix elements of our two-state Hamiltonian. Diagonalizing this Hamiltonian, we find the relative contribution of each spin-color configuration to the true heavy-meson ground state.

We have measured the charge asymmetry of muons produced in W boson decay as a function of muon pseudorapidity. The W bosons were produced in pp̄ collisions at √s = 1.8 TeV at the Fermilab Tevatron and recorded by the D⊘ detector during the run period 1992-1993 (run 1A) and 1994-1995 (run 1B). The combined data for both periods consists of 8831 W → μν decays with / ημ / < 1.0 selected from events corresponding to an integrated luminosity of 61.9 pb⁻¹ and 664 decays with 1.0 ≤ / ημ / < 1.6 corresponding to an integrated luminosity of 44.5 pb⁻¹.