42 research outputs found
An anomalous Wtb coupling at a linear collider
Differential cross sections of secondary particles in a process of top quark
pair production and decay into six fermions at a linear collider with an
unpolarized and a longitudinally polarized electron beam are computed to the
lowest order in the standard model and in the presence of an anomalous Wtb
coupling. It is illustrated that the latter has a little impact on the
differential cross sections. In particular, it is shown that the angular
distribution of a secondary lepton receives practically no contribution from
the anomalous Wtb coupling, even if the top quark is produced off shell and the
non-double resonance background contributions are taken into account. This
finding is in accordance with the decoupling theorem that has been proven in
literature in the narrow top quark width approximation.Comment: 11 pages, 9 figures, axodraw.st
SUSY-Induced CP Violation in Decays at Colliders
CP violation in the decays and from the production process e^-e^+ \to \ttbar is discussed. Since the
asymmetry proposed as a measure of CP violation vanishes even at the one-loop
level in the Standard Model (SM), it may be a useful tool to search for sources
of CP violation outside of the SM. As an illustration the asymmetry has been
computed within supersymmetric extensions of the SM. Prospects for its
measurement at future high-energy linear colliders are discussed.Comment: 17 pages, corrected former postscript output mistake
Using Back-Scattered Laser Beams to Detect CP Violation in the Neutral Higgs Sector
We demonstrate that the ability to polarize the photons produced by
back-scattering laser beams at a TeV scale linear \epem collider could make
it possible to determine whether or not a neutral Higgs boson produced in
photon-photon collisions is a CP eigenstate. The relative utility of different
types of polarization is discussed. Asymmetries that are only non-zero if the
Higgs boson is a CP mixture are defined, and their magnitudes illustrated for a
two-doublet Higgs model with CP-violating neutral sector.Comment: 15 pages, UCD-92-18, 4 figures, postscript figure files available by
request, uses phyzzx.te
Four-Fermi Effective Operators in Top-Quark Production and Decay
Effects of four-Fermi-type new interactions are studied in top-quark pair
production and their subsequent decays at future e^+e^- colliders.
Secondary-lepton-energy distributions are calculated for arbitrary longitudinal
beam polarizations. An optimal-observables procedure is applied for the
determination of new parameters.Comment: Polarized e^- plus unpolarized e^+ collisions were include
Gluon Fusion: A Probe of Higgs Sector CP Violation
We demonstrate that CP violation in the Higgs sector, \eg\ of a multi-doublet
model, can be directly probed using gluon-gluon collisions at the SSC. %
requires phyzzx.tex macro packageComment: UCD-93-
Electric Dipole Moments of Neutron and Electron in Two-Higgs-Doublet Model with Maximal violation
We study the electric dipole moments(EDM) of the neutron and the electron in
the two-Higgs-doublet model, in the case that symmetry is violated
maximally in the neutral Higgs sector. We take account of the Weinberg's
operator O_{3g}=GG\t G as well as the operator
for the neutron, and the Barr-Zee diagrams for the electron. It is found that
the predicted neutron EDM could be considerably reduced by the destructive
contribution of the two Higgs scalars to get the lower value than the
experimental bound. As to the electron EDM, the predicted value is smaller in
one order than the experimental one.Comment: 15pages, UWThPh-1994-48, AUE-08-94, US-94-06. The post-script files
of figures will be sent by request by electric mai
Using Decay Angle Correlations to Detect CP Violation in the Neutral Higgs Sector
We demonstrate that decay angle correlations in \taum\taup and t\anti t
decay modes could allow a determination of whether or not a neutral Higgs boson
is a CP eigenstate. Sensitivity of the correlations is illustrated in the case
of the \epem\rta Z \hn and \mupmum\rta \hn production processes for a
two-doublet Higgs model with CP-violating neutral sector. A very useful
technique for minimizing `depolarization-factor' suppressions of the
correlations in the t\anti t mode is introduced.Comment: 13 pages, phyzzx.tex macro, full postscript file including embedded
figure available at ftp://ucdhep.ucdavis.edu/gunion/cpasym.p
CP-Violating Lepton-Energy Correlation in e\bar{e}\to t\bar{t}
In order to observe a signal of possible CP violation in top-quark couplings,
we have studied energy correlation of the final leptons in at future linear colliders. Applying the
recently-proposed optimal method, we have compared the statistical
significances of CP-violation-parameter determination using double- and
single-lepton distributions. We have found that the single-lepton-distribution
analysis is more advantageous.Comment: Final version (to appear in Phys.Lett.B
Probing Top-Quark Couplings at Polarized NLC
The energy spectrum of the lepton(s) in e^+e^- --> tt-bar --> l^{+-}
...../l^+l^-..... at next linear colliders (NLC) is studied for arbitrary
longitudinal beam polarizations as a possible test of new physics in top-quark
couplings. The most general non-standard couplings for gamma-tt-bar, Ztt-bar
and Wtb vertices are considered. Expected precision of the
non-standard-parameter determination is estimated applying the
optimal-observable procedure.Comment: Final version, To appear in Phys. Rev.
Using Spin Correlations to Distinguish Zh from ZA at the International Linear Collider
We investigate how to exploit the spin information imparted to the Z boson in
associated Higgs production at a future linear collider as an aid in
distinguishing between CP-even and CP-odd Higgs bosons. We apply a generalized
spin-basis analysis which allowsus to study the possibilities offered by
non-traditional choices of spin projection axis. In particular, we find that
the Z bosons produced in association with a CP-even Higgs via polarized
collisions are in a single transverse spin-state (>90% purity) when we use the
Zh-transverse basis, provided that the Z~bosons are not ultra-relativistic
(speed <0.9c). This same basis applied to the associated production of a CP-odd
Higgs yields Z's that are an approximately equal mixture of longitudinal and
transverse polarizations. We present a decay angular distribution which could
be used to distinguish between the CP-even and CP-odd cases. Finally, we make a
few brief remarks about how this distribution would be affected if the Higgs
boson turns out to not be a CP-eigenstate.Comment: 48 pages, 18 figures, revtex