472 research outputs found
Decays of polarized top quarks to lepton, neutrino and jets at NLO QCD
We compute the differential and total rate of the semileptonic decay of
polarized top-quarks at
next-to-leading order (NLO) in the QCD coupling with an off-shell intermediate
boson. We present several normalized distributions, in particular those
that reflect the -spin analyzing powers of the lepton, the b-jet and the
boson at LO and NLO QCD.Comment: Latex, 22 page
Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders
We show how to observe sizable angular correlations between the decay
products of the top quark and those of the anti-top quark in top quark pair
production and decay at hadron colliders. These correlations result from the
large asymmetry in the rate for producing like-spin versus unlike-spin top
quark pairs provided the appropriate spin axes are used. The effects of new
physics at production or decay on these correlations are briefly discussed.Comment: 34 pages, revtex, including 12 uuencoded postscript figure
CP violation at colliders
The prospects of experimental detection of violation at and
colliders are reviewed. After a general discussion on the
quantities which can measure violation and on the implications of the
theorem, various possibilities of measuring violation arising
outside the standard model are taken up. violation in leptonic processes,
especially polarization effects in are discussed
next. violation in and production and decay is
also described. (Based on talk presented at the WHEPP3, Madras, January 1994).Comment: 20 pages, latex, no figures (only revision is the comment that the
article is based on a talk presented at WHEPP3, Madras, January 1994
Top Production in Hadron-Hadron Collisions and Anomalous Top-Gluon Couplings
We discuss the influence of anomalous tbar-t-G couplings on total and
differential tbar-t production cross sections in hadron-hadron collisions. We
study in detail the effects of a chromoelectric and a chromomagnetic dipole
moment, d' and \mu', of the top quark. In the d'-\mu' plane, we find a whole
region where the anomalous couplings give a zero net contribution to the total
top production rate. In differential cross sections, the anomalous moments have
to be quite sizable to give measurable effects. We estimate the values of d'
and \mu' which are allowed by the present Tevatron experimental results on top
production. A chromoelectric dipole moment of the top violates CP invariance.
We discuss a simple CP-odd observable which allows for a direct search for CP
violation in top production.Comment: footnote pg. 4 changed, acknowledgments extende
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.
Top Quark Pair Production and Decay including Spin Effects at Hadron Colliders: Predictions at NLO QCD
Top quark-antiquark () pairs will be produced copiously at the
Tevatron collider and in huge numbers at the LHC. This will make possible
detailed investigations of the properties and interactions of this quark
flavor. The analysis and interpretation of future data requires precise
predictions of the hadronic production of pairs and of their
subsequent decays. In this talk the reactions are considered and results are presented of our calculation
of the dilepton angular distribution at next-to-leading order QCD, keeping the
full dependence on the spins of the intermediate state. The angular
distribution is determined for different choices of reference axes that can be
identified with the and spin axes. While the QCD corrections to
the leading-order distribution turn out to be small in the case of the LHC, we
find them to be sizeable in the case of the Tevatron and find, moreover, the
angular distribution to be sensitive to the parton content of the proton.Comment: Talk given at 3rd Circum-Pan-Pacific Symposium on "High Energy Spin
Physics", Beijing, China, 8-13, 200
Top quark spin correlations at hadron colliders: Predictions at next-to-leading order QCD
The collider experiments at the Tevatron and the LHC will allow for detailed
investigations of the properties of the top quark. This requires precise
predictions of the hadronic production of pairs and of their
subsequent decays. In this Letter we present for the reactions the first calculation of the dilepton
angular distribution at next-to-leading order (NLO) in the QCD coupling,
keeping the full dependence on the spins of the intermediate state.
The angular distribution reflects the degree of correlation of the and
spins which we determine for different choices of and
spin bases. In the case of the Tevatron, the QCD corrections are sizeable, and
the distribution is quite sensitive to the parton content of the proton.Comment: 9 pages, 2 figure
CP Violation in the Top-Quark Pair Production at a Next Linear Collider
We provide a detailed, model-independent, study for CP violation effects due
to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment
(WDM) in the top-quark pair production via and two-photon annihilation
at a next linear collider (NLC). There are two methods in detecting CP
violation effects in these processes. One method makes use of measurements of
various spin correlations in the final decay products of the produced top-quark
pair, while the other is to measure various CP-odd polarization asymmetry
effects of the initial states. In the case only the first method can
be used, and in the case both methods can be employed. We
provide a complete classification of angular correlations of the and
decay products under CP and CP\tilde{T} which greatly faciliate CP
tests in the mode. Concentrating on the second method with the Compton
back-scattered high-energetic laser light off the electron or positron beam in
the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial
polarization configurations and apply them to investigating CP-violating
effects due to the top-quark EDM. With a typical set of experimental parameters
at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM
in the mode and the two-photon mode. Some model expectation values of
the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st
Master Integrals for Massless Three-Loop Form Factors: One-Loop and Two-Loop Insertions
The three-loop form factors in massless QCD can be expressed as a linear
combination of master integrals. Besides a number of master integrals which
factorise into products of one-loop and two-loop integrals, one finds 16
genuine three-loop integrals. Of these, six have the form of a bubble insertion
inside a one-loop or two-loop vertex integral. We compute all master integrals
with these insertion topologies.Comment: 12 pages, 1 figur
CP Nonconservation in at the Tevatron
The reaction is found to be rather rich in exhibiting
several different types of CP asymmetries. The spin of the top quark plays an
important role. Asymmetries are related to form factors arising from radiative
corrections of the production vertex due to non-standard physics. As
illustrations, effects are studied in two Higgs Doublet Models and in
Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that
appeared on some postscript previewers. No change in conten
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