Dr Elizabeth Gallas

Abstract:

We present a measurement of the t¯t production cross section in p¯p collisions at √s=1.8TeV by the D0 experiment at the Fermilab Tevatron. The measurement is based on data from an integrated luminosity of approximately 125pb−1 accumulated during the 1992–1996 collider run. We observe 39 t¯t candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7 ± 2.2 events. For a top quark mass of 173.3 GeV/c2, we measure the t¯t production cross section to be 5.5 ± 1.8 pb. © 1997 The American Physical Society.

Abstract:

We report on a search for pair production of a fourth generation charge -1/3 quark (b’) in pp collisions at s = 1.8 TeV by the DØ experiment at the Fermilab Tevatron using an integrated luminosity of 93 pb-1. Both b’ quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures γ + 3 jets + μ-tag and 2γ + 2 jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fraction that is well below theoretical expectations for a b’ decaying exclusively via FCNC for b’ masses up to mz + mb. © 1996 American Physical Society.

Abstract:

A search for new physics has been carried out in the channel pp → γγ + ET, as expected in various supersymmetric models. We require two photons with transverse energy EγT > 12 GeV and pseudorapidity |ηγ < 1.1. The distribution of missing transverse energy (ET) is consistent with background and no events have ET > 25 GeV. We set limits on production cross sections for selectron, sneutrino, and neutralino pairs, decaying into photons, which range from about 400 fb to 1 pb depending on the sparticle masses. A general limit of 185 fb (95% C.L.) is set on σ(pp → γγET + X), where eγT > 12 GeV, |ηγ| < 1.1, and ET > 25 GeV. © 1997 The American Physical Society.

Abstract:

We have searched for the pair production of first generation scalar leptoquarks in the eejj channel using the full data set (123pb−1) collected with the D0 detector at the Fermilab Tevatron during 1992-1996. We observe no candidates with an expected background of approximately 0.4 events. Comparing the experimental 95% confidence level upper limit to theoretical calculations of the cross section with the assumption of a 100% branching fraction of eq, we set a lower limit on the mass of a first generation scalar leptoquark of 225 GeV/c2. The results of this analysis rule out the interpretation of the excess of high Q2 events at DESY HERA as leptoquarks which decay exclusively to eq. © 1997 The American Physical Society.

Abstract:

The gauge boson pair production processes [Formula presented], [Formula presented], [Formula presented], and [Formula presented] were studied using [Formula presented] collisions corresponding to an integrated luminosity of approximately [Formula presented] at a center-of-mass energy of [Formula presented] TeV. Analysis of [Formula presented] production with subsequent [Formula presented] boson decay to [Formula presented] [Formula presented] is reported, including a fit to the [Formula presented] spectrum of the photons which leads to limits on anomalous [Formula presented] couplings. A search for [Formula presented] production with subsequent decay to [Formula presented] [Formula presented] is presented, leading to an upper limit on the [Formula presented] production cross section and limits on anomalous [Formula presented] and [Formula presented] couplings. A search for high [Formula presented] [Formula presented] bosons in [Formula presented] and [Formula presented] production is described, where one [Formula presented] boson decays to an electron and a neutrino and the second [Formula presented] boson or the [Formula presented] boson decays to two jets. A maximum likelihood fit to the [Formula presented] spectrum of [Formula presented] bosons resulted in limits on anomalous [Formula presented] and [Formula presented] couplings. A combined fit to the three data sets which provided the tightest limits on anomalous [Formula presented] and [Formula presented] couplings is also described. Limits on anomalous [Formula presented] and [Formula presented] couplings are presented from an analysis of the photon [Formula presented] spectrum in [Formula presented] events in the decay channels [Formula presented] of the [Formula presented] boson. © 1997 The American Physical Society.