WZWZ Production at eγe\gamma Colliders and Anomalous Quartic WWZγWWZ\gamma Coupling

We investigate the constraints on the anomalous quartic $W^{+}W^{-}Z\gamma$ gauge boson coupling through the process $e^{-}\gamma\to \nu_{e}W^{-}Z$. Considering incoming beam polarizations and the longitudinal and transverse polarization states of the final W and Z boson we find 95% confidence level limits on the anomalous coupling parameter $a_{n}$ with an integrated luminosity of 500 $fb^{-1}$ and $\sqrt{s}$=0.5, 1 TeV energies. We show that initial beam and final state polarizations improve the sensitivity to the anomalous coupling by up to factors of 2 - 3.5 depending on the energy.Comment: published versio

Single-top production at future ep colliders

The production of top quarks in single mode at future ep colliders is studied, the attention being mainly focused to the case of the proposed LEPXLHC collider. We are motivated to reanalyse such a process following the discovery of the top quark at Fermilab. Thanks to the measurement of its mass one is now able to establish more accurately the relevance of single top production for itself and for many other processes to which it may act as a background. In addition, the recent improvement of our knowledge of the quark and gluon dynamics inside the proton now allows one to pin down the dependence of single top production on the partonic structure functions. Both the leptonic and hadronic decay channels of the top quark are studied and compared to the yield of the corresponding irreducible background in presence of b-taggingComment: 28 pages, latex, epsfig, 10 postscript figures, complete paper available at ftp://axpa.hep.phy.cam.ac.uk/moretti/cavendish_9704 and at http://www.hep.phy.cam.ac.uk/theory/papers

Intermediate mass standard model Higgs boson at the proposed CERN LEP⊗\otimesLHC epep collider

The production of the \sm\ Higgs $\phi$ with intermediate mass at the proposed CERN LEP$\otimes$LHC $ep$ collider in $\gamma q(\bar q)\rightarrow W^\pm\phi q'(\bar q')$, $\gamma q(\bar q)\rightarrow Z^0\phi q(\bar q)$ and $g\gamma\rightarrow q\bar q\phi$ events is studied. This is done for all possible (massive) flavours of the quarks $q(q')$ and using photons generated via Compton back--scattering of laser light. We study signatures in which the Higgs decays to $b\bar b$--pairs and the electroweak vector bosons $W^\pm$ and $Z^0$ decay either hadronically or leptonically. All possible backgrounds to these signals are also computed. Flavour identification on $b$--jets is assumed. Explicit formulae for the helicity amplitudes of the above processes are given.Comment: 31 pages, Latex, 8 figures uuencoded, revised version, significant changes in the discussion of the results, in tables and figure

Constraints on anomalous quartic gauge boson couplings from nu(nu)over-bar gamma gamma and q(q)over-bar gamma gamma events at CERN LEP2

Anomalous quartic couplings between the electroweak gauge bosons may contribute to the nu(nu) over bar gammagamma and q (q) over bar gammagamma final states produced in e(+)e(-) collisions. This analysis uses the LEP2 OPAL data sample at center-of-mass energies up to 209 GeV. Event selections identify nu(nu) over bar gammagamma and q (q) over bar gammagamma events in which the two photons are reconstructed within the detector acceptance. The cross section for the process e(+)e(-)-->q (q) over bar gammagamma is measured. Averaging over all energies, the ratio of the observed e(+)e(-)-->q (q) over bar gammagamma cross section to the standard model expectation is R(data/SM)=0.92+/-0.07+/-0.04, where the errors represent the statistical and systematic uncertainties respectively. The nu(nu) over bar gammagamma and q (q) over bar gammagamma data are used to constrain possible anomalous W(+)W(-)gammagamma and ZZgammagamma couplings. Combining with previous OPAL results from the W(+)W(-)gamma final state, the 95% confidence level limits on the anomalous coupling parameters a(0)(Z), a(c)(Z), a(0)(W) and a(c)(W) are found to be -0.007 GeV-2<a(0)(Z)/Lambda(2)<0.023 GeV-2, -0.029 GeV-2<a(c)(Z)/Lambda(2)<0.029 GeV-2, -0.020 GeV-2<a(0)(W)/Lambda(2)<0.020 GeV-2, -0.052 GeV-2<a(c)(W)/Lambda(2)<0.037 GeV-2, where Lambda is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented