Dr Elizabeth Gallas

Abstract:

We present a search for Wbb̄ production in pp̄ collisions at √s = 1.96 TeV in events containing one electron, an imbalance in transverse momentum, and two b-tagged jets. Using 174 pb-1 of integrated luminosity accumulated by the D0 experiment at the Fermilab Tevatron collider, and the standard-model description of such events, we set a 95% C.L. upper limit on Wbb̄ production of 6.6 pb for b quarks with transverse momenta pTb > 20 GeV and bb̄ separation in pseudorapidity-azimuth space δRbb > 0.75. Restricting the search to optimized bb̄ mass intervals provides upper limits on WH production of 9.0-12.2 pb for Higgs-boson masses of 105-135 GeV. © 2005 The American Physical Society.

Abstract:

We present the results of a search for the flavor-changing neutral current decay Bs0 → μ+ μ-. using a data set with integrated luminosity of 240 pb-1 of pp̄ collisions at √s = 1.96 TeV collected with the D0 detector in run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be B(Bs0 → μ+ π-) ≤ 5.0 × 10-7 at the 95% C.L. assuming no contributions from the decay Bd0 → μ+ μ- in the signal region. This limit is the most stringent upper bound on the branching fraction Bs0 → μ+ μ- to date. © 2005 The American Physical Society.

Abstract:

Using the exclusive decay Bs0 → J/ψ (μ+μ-)φ (K+K-), we report the most precise single measurement of the Bs0 lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb-1 collected with the DO detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the Bs0 lifetime, τ(Bs0) = 1.444-0.090+0.098(stat) ± 0.020(sys) ps. We also report a measurement for the lifetime of the B0 meson using the exclusive decay B0 → J/ψ(μ+μ-) K*0(&92)(K+π-). We reconstruct 1370 signal candidates, obtaining τ(B0) = 1.473 -0.050+0.052(stat)±0.023(sys) ps, and the ratio of lifetimes, τ(Bs0)/τ(B0) = 0.980 -0.0.710.076(stat) ± 0.003(sys). © 2005 The American Physical Society.

Abstract:

We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb-1 of data collected by the DO experiment at the Fermilab Tevatron Collider in 2002-2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-to-lightest SUSY particle. © 2005 The American Physical.

Abstract:

We describe a measurement of the mass of the top quark from the purely hadronic decay modes of tt̄ pairs using all-jet data produced in pp̄ collisions at s=1.8 TeV at the Fermilab Tevatron Collider. The data, which correspond to an integrated luminosity of 110.2±5.8 pb-1, were collected with the DØ detector from 1992 to 1996. We find a top quark mass of 178.5±13.7(stat)±7.7(syst) GeV/c2. © 2004 Elsevier B.V. All rights reserved.