19 research outputs found
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
WW Production Cross Section and W Branching Fractions in e+e- Collisions at 189 GeV
From a data sample of 183 pb^-1 recorded at a center-of-mass energy of roots
= 189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are
selected. Assuming Standard Model W boson decay branching fractions, the W-pair
production cross section is measured to be sigmaWW = 16.30 +- 0.34(stat.) +-
0.18(syst.) pb. When combined with previous OPAL measurements, the W boson
branching fraction to hadrons is determined to be 68.32 +- 0.61(stat.) +-
0.28(syst.) % assuming lepton universality. These results are consistent with
Standard Model expectations.Comment: 22 pages, 5 figures, submitted to Phys. Lett.
Searches for prompt light gravitino signatures in e+ e- collisions at S**(1/2) = 189-GeV
Searches for final states expected in models with light gravitinos have been
performed, including experimental topologies with multi-leptons with missing
energy, leptons and photons with missing energy, and jets and photons with
missing energy. No excess over the expectations from the Standard Model has
been observed. Limits are placed on production cross-sections in the different
experimental topologies. Additionally, combining with searches for the
anomalous production of lepton and photon pairs with missing energy, results
are interpreted in the context of minimal models of gauge mediated SUSY
breaking. Exclusion limits are established at the 95% confidence level on the
supersymmetric particle masses; m-slepton > 83 GeV and m-neutralino > 85 GeV
for tan(beta)=2, m-stau > 69 GeV, m-selectron,-smu > 88 GeV and m-neutralino >
76 GeV for tan(beta)=20.Comment: 19 pages, 6 figures, submitted to Phys. Lett.
Search for single top quark production at LEP-2
A search for single top quark production via flavour changing neutral
currents (FCNC) was performed with data collected by the OPAL detector at the
e+e- collider LEP. Approximately 600 pb-1 of data collected at sqrt(s) = 189 -
209 GeV were used to search for the FCNC process e+ e- -> tc(u) -> bWc(u). This
analysis is sensitive to the leptonic and the hadronic decay modes of the W
boson. No evidence for a FCNC process is observed. Upper limits at the 95%
confidence level on the single top production cross-section as a function of
the centre-of-mass energy are derived. Limits on the anomalous coupling
parameters kappa_gamma and kappa_Z are determined from these results.Comment: 21 pages, 4 figures, Submitted to Phys. Lett.
Search for the standard model Higgs boson in e+ e- collisions at s**(1/2) approximately = 192-GeV - 209-GeV
A search for the Standard Model Higgs boson has been performed with the OPAL
detector at LEP based on the full data sample collected at sqrt(s) = 192-209
GeV in 1999 and 2000, corresponding to an integrated luminosity of
approximately 426 pb-1. The data are examined for their consistency with the
background-only hypothesis and various Higgs boson mass hypotheses. A lower
bound of 109.7 GeV is obtained on the Higgs boson mass at the 95% confidence
level. At higher masses, the data are consistent with both the background and
the signal-plus-background hypotheses.Comment: 19 pages, 7 figures, Accepted by Physics Letters