158 research outputs found
Signals of CP Violation in Distributions of Top-Quark Decay Products at Linear Colliders
Angular and energy distributions for leptons and bottom quarks in the process
e+e- --> t tbar --> l/b ... have been calculated assuming the most general
top-quark couplings. The double distributions depend both on modification of
the top-quark production and tbW decay vertices. However, the leptonic angular
distribution turned out to be insensitive to non-standard parts of tbW vertex.
The method of optimal observables have been used to estimate sensitivity of
future measurements at linear e+e- collidersComment: 7 pages, LaTex, 1 figure, talk given at PASCOS '99, Lake Tahoe,
California, December 10-16, 1999, typos in the reference list correcte
Remarks on the Value of the Higgs Mass from the Present LEP Data
We perform a detailed comparison of the present LEP data with the one-loop
standard-model predictions. It is pointed out that for GeV the
``bulk'' of the data prefers a rather large value of the Higgs mass in the
range 500-1000 GeV, in agreement with the indications from the W mass. On the
other hand, to accommodate a light Higgs it is crucial to include the more
problematic data for the F-B asymmetry. We discuss further improvements
on the data taking required to obtain a firm conclusion.Comment: LaTeX Some comments were added to the note in relation to the new
data on the top-quark mass
Addendum to: Search for anomalous top-gluon couplings at LHC revisited
In our latest paper "Search for anomalous top-gluon couplings at LHC
revisited" in Eur. Phys. J. C65 (2010), 127-135 (arXiv:0910.3049 [hep-ph]), we
studied possible effects of nonstandard top-gluon couplings through the
chromoelectric and chromomagnetic moments of the top quark using the total
cross section of ppbar/pp --> ttbar X at Tevatron/LHC. There we pointed out
that LHC data could give a stronger constraint on those two parameters, which
would be hard to obtain from Tevatron data alone. We show here the first CMS
measurement of this cross section actually makes it possible.Comment: 5 pages, 1 figure, LaTeX2e, Final version (to appear in Eur. Phys. C
Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization
We investigate the possibilities of studying new physics in various processes
of t-quark production using kinematical distributions of the secondary lepton
coming from decay of t quarks. We show that the angular distributions of the
secondary lepton are insensitive to the anomalous tbW vertex and hence are pure
probes of new physics in a generic process of t-quark production. The energy
distribution of the lepton is distinctly affected by anomalous tbW couplings
and can be used to analyze them independent of the production process of t
quarks. The effects of t polarization on the distributions of the decay lepton
are demonstrated for top-pair production process at a gamma-gamma collider
mediated by a heavy Higgs boson.Comment: 15 pages, 7 figures, uses axodraw.sty (included), references added.
v3 to appear in Journal of High Energy Physics. Incorporates minor changes in
the discussion on radiative corrections which do not affect the results. Typo
in reference correcte
QED Corrections to the Scattering of Solar Neutrinos and Electrons
We discuss recent calculations of the O(alpha) QED corrections to the recoil
electron energy spectrum in neutrino electron scattering, and to the spectrum
of the combined energy of the recoil electron and a possible accompanying
photon emitted in the scattering process. We then examine the role of these
corrections in the interpretation of precise measurements from solar neutrino
electron scattering experiments.Comment: (16 Pages, 4 Figures) Presented at the Symposium in Honor of
Professor Alberto Sirlin's 70th Birthday: ``50 Years of Precision Electroweak
Physics'', New York University, October 27-28, 200
Incorporation of QCD Effects in Basic Corrections of the Electroweak Theory
We study the incorporation of QCD effects in the basic electroweak
corrections \drcar, \drcarw, and \dr. They include perturbative
\Ord{\alpha\alpha_s} contributions and threshold effects. The latter
are studied in the resonance and Green-function approaches, in the framework of
dispersion relations that automatically satisfy relevant Ward identities.
Refinements in the treatment of the electroweak corrections, in both the \ms\
and the on-shell schemes of renormalization, are introduced, including the
decoupling of the top quark in certain amplitudes, its effect on
\hat{e}^2(\mz) and \sincarmz, the incorporation of recent results on the
leading irreducible \Ord{\alpha^2} corrections, and simple expressions for the
residual, i.e.\ ``non-electromagnetic'', parts of \drcar, \drcarw, and \dr. The
results are used to obtain accurate values for \mw\ and \sincarmz, as functions
of \mt\ and \mh. The higher-order effects induce shifts in these parameters
comparable to the expected experimental accuracy, and they increase the
prediction for \mt\ derived from current measurements. The \ms\ and the
on-shell calculations of \dr, in a recently proposed formulation, are compared
and found to be in excellent agreement over the wide ranges 60\GeV \leq \mh
\leq 1 \TeV, \mz \leq \mt \leq 250 \GeV.Comment: 51 pages (needs doublespace, equations, and cite styles
Dilepton azimuthal correlations in tt production
The dilepton azimuthal correlation, namely the difference phi between the azimuthal
angles of the positive and negative charged lepton in the laboratory frame, provides
a stringent test of the spin correlation in tt production at the Large Hadron Collider. We
introduce a parameterisation of the differential cross section dalpha=dphi in terms of a Fourier
series and show that the third-order expansion provides a su ciently accurate approximation.
This expansion can be considered as a `bridge' between theory and data, making it
very simple to cast predictions in the Standard Model (SM) and beyond, and to report
measurements, without the need to provide the numbers for the whole binned distribution.
We show its application by giving predictions for the coeffcients in the presence of
(i) an anomalous top chromomagnetic dipole moment; (ii) an anomalous tbW interaction.
The methods presented greatly facilitate the study of this angular distribution, which is of
special interest given the 3:2(3:7) deviation from the SM next-to-leading order prediction
found by the ATLAS collaboration in Run 2 data.This work has been supported by MINECO Project FPA 2013-47836-C3-2-P (including
ERDF)
Higgs Boson Production and Weak Boson Structure
The influence of the QCD structure of the weak bosons on the Higgs boson
production in - scattering is studied. The energy and Higgs boson mass
dependence of the cross-section, following from the new contributions, is
calculated.Comment: 8 pages, 3 figures, compressed uuencoded Postscript fil
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