Dr Elizabeth Gallas

Abstract:

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at √s = 630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

We determine the top quark mass mt using tt̄ pairs produced in the DØ deteetor by √s = 1.8 TeV pp̄ collisions in a 125 ph-1 exposure at the Fermilab Tevatron. We make a two constraint fit to mt in tt̄→bW+b̄W- final states with one W boson decaying to qq̄ and the other to eν or μν. Likelihood fits to the data yield mt(l+jets) = 173.3±5.6 (stat) ± 5.5 (syst) GeV/c2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain mt = 172.1 ± 5.2 (stat) ± 4.9 (syst) GeV/c2. An alternate analysis, using three constraint fits to fixed top quark masses, gives mt(l + jets) = 176.0 ± 7.9 (stat) ± 4.8 (syst) GeV/c2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.

Abstract:

The results of a search for W boson pair production in pp̄ collisions at √s = 1.8 TeV with subsequent decay to eμ, ee, and μμ channels are presented. Five candidate events are observed with an expected background of 3.1 ± 0.4 events for an integrated luminosity of approximately 97 pb^-1. Limits on the anomalous couplings are obtained from a maximum likelihood fit of the ET spectra of the leptons in the candidate events. Assuming identical WWγ and WWZ couplings, the 95% C.L. limits are -0.62<Δκ<0.77 (λ = 0) and -0.53<λ <0.56 (Δκ = 0) for a form factor scale Λ= 1.5 TeV.

Abstract:

We report on a search for the trilepton decay signature from the associated production of supersymmetric gaugino pairs, χ∼±1χ∼02, within the context of minimal supersymmetric models that conserve R parity. This search uses 95 pb−1 of pp− data taken at s = 1.8 TeV with the D0 detector. No evidence of a trilepton signature has been found, and a limit on the product of cross section times branching fraction to trileptons is given as a function of χ∼±1 mass. © 1998 The American Physical Society.

Abstract:

Prototypes of the FERMI system have been used to read out a prototype of the ATLAS hadron calorimeter in a beam test at the CERN SPS. The FERMI read-out system, using a compressor and a sampling ADC, is compared to a standard charge integrating read-out by measuring the energy resolution of the calorimeter separately with the two systems on the same events. Signal processing techniques have been designed to optimize the treatment of FERMI data. The resulting energy resolution is better than the one obtained with the standard read-out. © 1998 Elsevier Science B.V. All rights reserved.