4 research outputs found
Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay
We report on a search for pair production of a fourth generation charge -1/3
quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron
using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay
via flavor changing neutral currents (FCNC). The search uses the signatures
gamma + 3 jets + mu-tag and 2 gamma + 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' quark decaying exclusively via FCNC for b' quark masses
up to m(Z) + m(b).Comment: Eleven pages, two postscript figures, submitted to Physical Review
Letter
Measurement of the Top Quark Pair Production Cross Section in pbarp Collisions
We present a measurement of the ttbar production cross section in ppbar
collisions at root(s) = 1.8TeV by the D0 experiment at the Fermilab Tevatron.
The measurement is based on data from an integrated luminosity of approximately
125 pb^-1 accumulated during the 1992-1996 collider run. We observe 39 ttbar
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 173.3GeV/c^2,
we measure the ttbar production cross section to be 5.5+-1.8 pb.Comment: 11 pages with 3 encapsulated PostScript figures and 2 PostScript
table included in the body of the articl
Direct Measurement of the Top Quark Mass
We measure the top quark mass m_t using t tbar pairs produced in the D0
detector by root(s) = 1.8 TeV p pbar collisions in a 125 pb^-1 exposure at the
Fermilab Tevatron. We make a two constraint fit to m_t in t tbar --> b W^+ bbar
W^- final states with one W decaying to q qbar and the other to e nu or mu nu.
Events are binned in fit mass versus a measure of probability for events to be
signal rather than background. Likelihood fits to the data yield m_t = 173.3 +-
5.6 (stat) +- 6.2 (syst) GeV/c^2.Comment: 11 pages with 3 encapsulated PostScript figures and 1 encapsulated
PostScript table included in the body of the articl
Search for Diphoton Events with Large Missing Transverse Energy in proton-antiproton collisions at sqrt(s) = 1.8 TeV
A search for signals of new physics has been carried out in the channel p
pbar -> gamma gamma + ETmiss. This signature is expected in various recently
proposed supersymmetric (SUSY) models. We observe 842 events with two photons
having transverse momentum ET(g) > 12 GeV and pseudorapidity |eta(g)| < 1.1. Of
these, none have missing transverse energy (ETmiss) in excess of 25 GeV. The
distribution of ETmiss is consistent with that of the expected background. We
therefore set limits on production cross sections for selectron, sneutrino and
neutralino pairs, decaying into photons. The limits 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 sigma.B(pbar p -> gamma gamma ETmiss + X) where ET(g) > 12 GeV, |eta(g)|
25 GeV.Comment: 6 pp, LaTeX, 2 postscript figures. Submitted to Physical Review
Letter