Dr Elizabeth Gallas

Abstract:

We have searched for a heavy neutral gauge boson, Z′, using the decay channel Z′ → ee. The data were collected with the DØ detector at the Fermilab Tevatron during the 1992-1993 pp̄ collider run at √s = 1.8 TeV from an integrated luminosity of 15 ± 1 pb^-1. Limits are set on the cross section times branching ratio for the process pp̄ → Z′ → ee as a function of the Z′ mass. We exclude the existence of a Z′ of mass less than 490 GeV/c², assuming a Z′ with the same coupling strengths to quarks and leptons as the standard model Z boson.

Abstract:

We report on a search for right-handed W bosons (WR) with mass greater than 200 GeV/c². We used data collected with the D0 detector at the Fermilab Tevatron pp¯ collider at √s = 1.8 TeV to search for WR decays into an electron and a massive right-handed neutrino WR ^±→e^±NR. Using the inclusive electron data, we set mass limits independent of the NR decay: mWR>650 GeV/c² and mWR>720 GeV/c² at the 95% confidence level, valid for mNR<1/2 mWR and mNR≪mWR, respectively. The latter also represents a new lower limit on the mass of a heavy left-handed W boson (W’) decaying into eν. In addition, limits on mWR valid for larger values of the NR mass are obtained assuming that NR decays to an electron and two jets. © 1996 The American Physical Society.

Abstract:

We have studied J/ψ production in pp̄ collisions at √s = 1.8 TeV with the DØ detector at Fermilab using μ⁺/μ^- data. We have measured the inclusive J/ψ production cross section as a function of J/ψ transverse momentum, pT. For the kinematic range pT > 8 GeV/c and |η\ < 0.6 we obtain σ(pp̄ → J/ψ + X) ·Br(J/ψ → μ⁺μ^-) = 2.08 ± 0.17(stat) ± 0.46(syst) nb. Using the muon impact parameter we have estimated the fraction of J/ψ mesons coming from B meson decays to be fb = 0.35 ± 0.09(stat)±0.10(syst) and inferred the inclusive b production cross section. From the information on the event topology the fraction of nonisolated J/ψ events has been measured to be fnonisol = 0.64 ± 0.08(stat)±0.06(syst). We have also obtained the fraction of J/ψ events resulting from radiative decays of χc states, fχ = 0.32 ± 0.07(stat)±0.07(syst). We discuss the implications of our measurements for charmonium production processes.

Abstract:

This study reports the first measurement of the azimuthal decorrelation between jets with pseudorapidity separation up to five units. The data were accumulated using the D0 detector during the 1992–1993 collider run of the Fermilab Tevatron at √s=1.8 TeV. These results are compared to next-to-leading order (NLO) QCD predictions and to two leading-log approximations (LLA) where the leading-log terms are resummed to all orders in αS. The final state jets as predicted by NLO QCD show less azimuthal decorrelation than the data. The parton showering LLA Monte Carlo HERWIG describes the data well; an analytical LLA prediction based on Balitsky-Fadin-Kuraev-Lipatov resummation shows more decorrelation than the data. © 1996 The American Physical Society.

Abstract:

A study of the particle multiplicity between jets with large rapidity separation has been performed using the D0 detector at the Fermilab Tevatron pp^¯ Collider operating at √s = 1.8 TeV. A significant excess of low-multiplicity events is observed above the expectation for color-exchange processes. The measured fractional excess is 1.07±0.10(stat)^+0.25−0.13(syst)%, which is consistent with a strongly interacting color-singlet (colorless) exchange process and cannot be explained by electroweak exchange alone. A lower limit of 0.80% (95% C.L.) is obtained on the fraction of dijet events with color-singlet exchange, independent of the rapidity gap survival probability. © 1996 The American Physical Society.