548 research outputs found
On the top-antitop invariant mass spectrum at the LHC from a Higgs boson signal perspective
We investigate the effect of one-loop corrections of on the invariant mass spectrum at the Large
Hadron Collider (LHC) in presence of both resonant and non-resonant Higgs boson
effects. We show that corrections of involving a
non-resonant Higgs boson are comparable to or even larger than those involving
interference with the s-channel resonant Higgs boson amplitude and that both of
these are subleading with respect to all other (non-Higgs) diagrams through
that order. We also compute the contribution through of resonant Higgs boson production (i.e. Higgs
production via fusion) as well as the pure QCD ones of . Altogether, we show that the well known peak-dip structure of
the spectrum emerging from interference effects between the
-channel -induced Leading Order (LO) QCD diagrams and the one due to a
Higgs boson in s-channel via -fusion is drastically swamped by the
remainder of the terms of discussed above.Comment: 6 pages, 8 figure
Weak dipole moment of in collisions with longitudinally polarized electrons
It is pointed out that certain CP-odd momentum correlations in the production
and subsequent decay of tau pairs in collisions get enhanced when the
is longitudinally polarized. Analytic expressions for these correlations
are obtained for the single-pion decay mode of when have
a ``weak" dipole form factor (WDFF) coupling to . For collisions
at the peak, a sensitivity of about 1-5\mbox{ cm} for
the WDFF can be reached using a {\em single} decay
channel, with 's likely to be available at the SLC at Stanford with
polarization of 62\%-75\%.Comment: 9 pages, Latex, PRL-TH-93/17 (Revised
Strong and Electro-Weak Supersymmetric Corrections to Single Top Processes at the Large Hadron Collider
We present the one-loop corrections originating from Quantum Chromo-Dynamics
(QCD) and Electro-Weak (EW) interactions of Supersymmetric (SUSY) origin within
the Minimal Supersymmetric Standard Model (MSSM) to the single-top processes bq
-> tq' and qbar q' -> tbar b. We illustrate their impact onto top quark
observables accessible at the Large Hadron Collider (LHC) in the 't+jet' final
state, such as total cross section, several differential distributions and
left-right plus forward-backward asymmetries. We find that in many instances
these effects can be observable for planned LHC energies and luminosities,
quite large as well as rather sensitive to several MSSM parameters.Comment: 22 pages, 10 figures; added a brief comment on the dependence of
results on the value of top mass; corrected typo
T-odd correlations from CP violating anomalous top-quark couplings revisited
We revisit the effect of CP violating anomalous top-quark couplings in
production and decay. We consider production through
gluon fusion (and light annihilation) followed by top-quark decay
into or . We find explicit analytic expressions for all the
triple products generated by the anomalous couplings that fully incorporate all
spin correlations. Our results serve as a starting point for numerical
simulations for the LHC.Comment: minor typos correcte
Measurement of the electric dipole moment using longitudinal polarization of beams
Certain CP-odd momentum correlations in the production and subsequent decay
of pairs in collisions are enhanced significantly when the
and beams are longitudinally polarized. These may be used to probe
the real and imaginary parts of , the electric dipole moment of
the . Closed-form expressions for these ``vector correlations'' and the
standard deviation of the operators defining them due to standard model
interactions are presented for the two-body final states of decays. If
42\% average polarization of each beam is achieved, as proposed for the
tau-charm factories, with equal integrated luminosities for each sign of
polarization and a total yield of pairs, it is
possible to attain sensitivities for of , , cm respectively and for of , , cm respectively at the three operating center-of-mass energies of
3.67, 4.25 and 10.58 GeV. These bounds emerge when the effects of a posible
weak dipole form factor are negligible as is the case when it is of
the same order of magnitude as . Furthermore, in such a
polarization experiment where different polarizations are possible, a
model-independent disentangling of their individual effects is possible, and a
technique to achieve this is described. A strong longitudinal polarization
physics programme at the tau-charm factory appears warranted.Comment: 30 pages, latex, no figure
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 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
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
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
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.
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