Dr Elizabeth Gallas

Abstract:

We report a new measurement of the tt̄ production cross section in pp̄ collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using 425pb-1 of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the tt̄ content of the sample by tagging b jets with a secondary vertex tagging algorithm, the tt̄ production cross section is measured to be σpp̄→tt̄+X=6.6±0.9(stat+syst) ±0.4(lum)pb. This cross section is the most precise D0 measurement to date for tt̄ production and is in good agreement with standard model expectations. © 2006 The American Physical Society.

Abstract:

The DØ experiment uses a dedicated data acquisition system to collect, archive, monitor, and distribute the information necessary to normalize triggered data for physics analyses. This system has been in place since the beginning of Run 2 of the Fermilab Tevatron collider in 2001 and provides real-time feedback on the instantaneous and triggered luminosities in the DØ and Tevatron control rooms, as well as the status reports needed for smooth operation of the experiment. This paper describes the architecture and the implementation of this system.

Abstract:

We measure the dimuon charge asymmetry A in pp̄ collisions at a center of mass energy s=1960GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0fb-1. Assuming that the asymmetry A is due to asymmetric B0↔B̄0 mixing and decay, we extract the CP-violation parameter of B0 mixing and decay: ( B0)1+| B0|2=AB04=-0.0023±0.0011(stat)±0.0008(syst).AB0 is the dimuon charge asymmetry from decays of B0B̄0 pairs. The general case, with CP violation in both B0 and Bs0 systems, is also considered. Finally we obtain the forward-backward asymmetry that quantifies the tendency of μ+ to go in the proton direction and μ- to go in the antiproton direction. The results are consistent with the standard model and constrain new physics. © 2006 The American Physical Society.

Abstract:

A search for direct production of scalar bottom quarks (b) is performed with 310pb-1 of data collected by the D0 experiment in pp̄ collisions at s=1.96TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (χ∼10), with χ∼10 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (mb∼, mχ∼10) mass plane, improving significantly upon the results from run I of the Tevatron. © 2006 The American Physical Society.

Abstract:

We present a search for a neutral particle, pair produced in pp̄ collisions at s=1.96TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses 380pb-1 of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair-production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4×10-11s, we exclude values greater than 0.14 pb (95 C.L.). These results are used to limit the interpretation of NuTeV's excess of dimuon events. © 2006 The American Physical Society.