21 research outputs found
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
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
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-
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 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
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
CP-Violation in Bosonic Sector of SM with two Higgs Doublets
We investigate CP-violation effects in the bosonic sector of the Standard
Model (SM) with two Higgs doublets. First we calculate the mass eigenstates of
the physical neutral Higgses for small but nonzero CP-violation parameter
, and then a ``forward-backward'' asymmetry for the
decay that would be a signal of CP-violation. Although the
effects are in general small (), turns out to be a rather clean signal of
CP-violation, since neither the CP-conserving final state interactions nor the
direct production background events contribute to . The process is
a counterexample to the widespread belief that CP-violation processes must
involve fermions. The CKM-type CP-violation effects that could in principle
also contribute to are negligible. The nonzero
could possibly be detected at some later stage in future colliders such as LHC
or SSC.Comment: 11 pages (standard LaTeX), 3 figures (available from the author),
DO-TH 93-1
Direct CP Violation in Angular Distribution of Decays
We show that the study of certain observables in the angular distribution in
provide clear test for CP vioaltion beyond the Standard
Model. These observables vanish in SM, but in models beyond SM some of them can
be large enough to be measured at B factories.Comment: 7 pages, Revte
Prospects for Direct CP Violaton in Exclusive and Inclusive Charmless B decays
Within the Standard Model, CP rate asymmetries for could
reach 10%. With strong final state phases, they could go up to 20--30%, even
for mode which would have opposite sign. We can account for
, and rate data with new physics enhanced
color dipole coupling and destructive interference. Asymmetries could reach
40--60% for and modes and are all of the same sign. We are
unable to account for rate. Our inclusive study supports our
exclusive results.Comment: Minor changes, correct a small bug in Fig. 1(b). Version to appear in
Phys. Rev. Let
Final-State-Interaction Simulation of T-Violation in the Top-Quark Semileptonic Decay
The standard electroweak final-state interaction induces a false T-odd
correlation in the top-quark semileptonic decay. The correlation parameter is
calculated in the standard model and found to be considerably larger than those
that could be produced by genuine T-violation effects in a large class of
theoretical models.Comment: 14 pages, 1 diagram (not included