Dr Elizabeth Gallas

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 E^γT > 12 GeV and pseudorapidity |η^γ < 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 e^γT > 12 GeV, |η^γ| < 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.

Abstract:

We have measured the ZZγ and ZZγ couplings by studying 13.1 pb−1 of pp¯→Etγ+ X data at √s = 1.8 TeV with the Dø detector at the Fermilab Tevatron Collider. This is the first study of hadronic Zγ production in the neutrino decay channel. Combining this measurement with our previous results using Z→ee and μμ yields the most stringent 95% C.L. limits to date on anomalous couplings: |h30Z|<0.4, |h40Z|<0.06 (λ=750 GeV. © 1997 The American Physical Society.