63 research outputs found
Origem, disseminação, morfologia e fenologia.
Origem e disseminação; Morfologia: Semente, Talo e coroa, Folha, Flor, Desenvolvimento floral e polinização, Fruto; Fenologi
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.
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]
Bounds on Radii and Magnetic Dipole Moments of Quarks and Leptons from LEP, SLC and HERA
Leptons, quarks and gauge bosons are assumed to be pointlike particles in the
Standard Model. Stringent bounds on the radii of quarks and leptons and their
weak anomalous magnetic moments can be derived from the high-precision
measurements at LEP and SLC. We find a model-independent bound of R\lsim
10^{-17}cm for quark and lepton radii. HERA will provide complementary
information on the electromagnetic static properties of the quarks and the
parameters of the charged quark currents.Comment: 10 pages,latex, 1 ps-figure and style files included as uuencoded
compressed file
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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