65 research outputs found
TAU-PAIR PRODUCTION VIA PHOTON-PHOTON COLLISIONS AT LEP
We point out that the cross-section for the process at LEP is large enough to allow for a study of the anomalous
electromagnetic couplings of the lepton. We show that the present bounds
on the magnetic dipole moment can be improved and that competitive bounds can
be obtained for the electric dipole moment using the data taken from 1992 to
1994. Finally, we briefly discuss the improvements that can be obtained at LEP
II.Comment: 9 pages, latex, 2 figure
Weak magnetic dipole moments in two-Higgs-doublet models
We investigate the effects of the new scalars in a two-Higgs-doublet model on
the weak magnetic dipole moments of the fermions at the peak.
Proportionality of the Yukawa couplings to the fermion masses, and to
, makes such effects more important for the third family, and
potentially relevant. For the lepton, the new diagrams are suppressed by
, or by powers of , but may still
be comparable to the SM electroweak contributions. In contrast, we find that
the new contributions for the bottom quark may be much larger than the SM
electroweak contributions. These new effects may even compete with the gluonic
contribution, if the extra scalars are light and is large. We also
comment on the problem of the gauge dependence of the vertex, arising when the
is off mass shell. We compute the contributions from the new scalars to the
magnetic dipole moments for top-quark production at the NLC, and for bottom and
production at LEP2. In the case of the top, we find that the SM
electroweak and gluonic contributions to the vertex are
comparable. The new contributions may be of the same order of magnitude as the
standard-model ones, but not much larger.Comment: 17 pages, LaTex, 8 figures available upon reques
Can We Observe Weak Anomalous Couplings of Heavy Quarks Through Three Jet Events?
The rates and corresponding jet distributions for the decay
and the process may be sensitive to anomalous dipole-like
couplings of heavy quarks to the photon and . In the -quark case, after
updating our previous analysis on the constraints imposed by current
experiments on anomalous couplings, we show that the variation of
these couplings within their presently allowed ranges leads to rather minor
modifications to the Standard Model expectations for
observables. In the -quark case, significant deviations from the Standard
Model predictions for production at the Next Linear Collider are
possible.Comment: 26 pages with 9 embedded figures; gzipped, uuencoded postscript file.
To obtain a copy of this paper send e-mail to [email protected]
A consistent treatment for pion form factors in space-like and time-like regions
We write down some relevant matrix elements for the scattering and decay
processes of the pion by considering a quark-meson vertex function. The pion
charge and transition form factors , , and
are extracted from these matrix elements using a relativistic
quark model on the light-front. We found that, the form factors and
in the space-like region agree well with experiment.
Furthermore, the branching ratios of all observed decay modes of the neutral
pion, that are related to the form factors and
in the time-like region, are all consistent with the data as
well. Additionally, in the time-like region, which deals with the
nonvalence contribution, is also discussed.Comment: 24 pages, 6 figures, to appear in Phys. Rev.
Mapeamento de coletas antigas de acessos de espécies forrageiras nativas do Sul do Brasil.
O trabalho consistiu na anĂĄlise de cadernetas de coleta de campo antigas da Embrapa PecuĂĄria Sul, compilando os dados de longitude, atitude e altitude de 205 acessos de Bromus auleticus, Paspalum dilatatum, P. notatum, P. pumilum e P. urvillei.Zootec
W ANOMALOUS MOMENTS AND THE POLARIZATION ASYMMETRY ZERO IN gamma e --> W nu
We show from general principles that there must be a center of mass energy,
, where the polarization asymmetry for circularly-polarized photon and
electron beams vanishes. In the case of the Standard Model, the crossing point
where the asymmetry changes sign occurs in Born approximation at GeV. We demonstrate the sensitivity
of the position of the polarization asymmetry zero to modifications of the SM
trilinear coupling. Given reasonable assumptions for the
luminosity and energy range for the Next Linear Collider(NLC) with a
backscattered laser beam, we show that the zero point, , of the
polarization asymmetry may be determined with sufficient precision to constrain
the anomalous couplings of the to better than the 1\% level at CL.
In addition to the fact that only a limited range of energy is required, the
polarization asymmetry measurements have the important advantage that many of
the systematic errors cancel in taking cross section ratios. The position of
the zero thus provides an additional weapon in the arsenal used to probe
anomalous trilinear gauge couplings.Comment: 21 pages, uuencoded postscript file. For hard copy, send e-mail to
[email protected]
Search for Manifestations of New Physics in Fermion-Pair Production at LEP
The measurements of hadron and lepton-pair production cross sections and
leptonic forward-backward asymmetries performed with the L3 detector at
centre-of-mass energies between 130 GeV and 189 GeV are used to search for new
physics phenomena such as: contact interactions, exchange of virtual
leptoquarks, scalar quarks and scalar neutrinos, effects of TeV strings in
models of quantum gravity with large extra dimensions and non-zero sizes of the
fermions. No evidence for these phenomena is found and new limits on their
parameters are set
Polarized \Lambda_b \to X_c \tau \nu in the SM and THDM
The inclusive rate and spectrum for a polarized -baryon to
decay to charm hadronic final states and leptons in the SM and a
two-Higgs doublet model are computed.The QCD corrections to
spectrum in the two-Higgs model are also given.Comment: Revtex,11 pages,5 figure
eta-prime Meson Production in Nucleon-Nucleon Collisions Near The Threshold
The production of mesons in the reactions and at threshold-near energies is analyzed within a covariant effective
meson-nucleon theory. The description of cross section and angular
distributions of the available data in this kinematical region in the
channel is accomplished by including meson currents and nucleon currents with
the resonances , and . Predictions
for the channel are given. The di-electron production from subsequent
Dalitz decay is also
calculated and numerical results are presented for intermediate energy and
kinematics of possible experiments with HADES, CLAS and KEK-PS
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