169 research outputs found
On the structure of the X(1835) baryonium
The measurement by the BES collaboration of J/psi -> gamma p pbar decays
indicates an enhancement at the p-pbar threshold. In another experiment BES
finds a peak in the invariant mass of pi-mesons produced in the possibly
related decay J/psi -> gamma pi+ pi- eta'. Using a semi-phenomenological
potential model which describes all the N-Nbar scattering data, we show that
the explanation of both effects may be given by a broad quasi-bound state in
the spin and isospin singlet S wave. The structure of the observed peak is due
to an interference of this quasi-bound state with a background amplitude and
depends on the annihilation mechanism.Comment: 7 pages, 7 figures, this version corresponds to the published paper
in Phys. Rev. C: minor corrections done and in section 5 suggestions of
experiments to confirm the link of the X(1835) to the antiproton-proton
syste
A combined study of the pion's static properties and form factors
We study consistently the pion's static observables and the elastic and
\gamma*\gamma -> \pi^0 transition form factors within a light-front model.
Consistency requires that all calculations are performed within a given model
with the same and single adjusted length or mass-scale parameter of the
associated pion bound-state wave function. Our results agree well with all
extent data including recent Belle data on the \gamma*\gamma -> \pi^0 form
factor at large q^2, yet the BaBar data on this transition form factor resists
a sensible comparison. We relax the initial constraint on the bound-state wave
function and show the BaBar data can partially be accommodated. This, however,
comes at the cost of a hard elastic form factor not in agreement with
experiment. Moreover, the pion charge radius is about 40% smaller than its
experimentally determined value. It is argued that a decreasing charge radius
produces an ever harder form factor with a bound-state amplitude difficultly
reconcilable with soft QCD. We also discuss why vector dominance type models
for the photon-quark vertex, based on analyticity and crossing symmetry, are
unlikely to reproduce the litigious transition form factor data.Comment: 14 pages, 7 figures, 2 Tables; minor changes; 2 new references added
(Ref. 54 and 57); version to be published in Few Body Physic
Pseudoscalar-scalar transition form factors in covariant light front dynamics
In an explicitly covariant light-front formalism, we analyze transition form
factors between pseudoscalar and scalar mesons. Application is performed in
case of the transition in the full available transfer momentum
range .Comment: 4 pages, 4 figures. Talk given at the XXXIII International Conference
on High Energy Physics, ICHEP06, Moscow, 26 July-02 Augus
Insights into the quark-gluon vertex from lattice QCD and meson spectroscopy
By comparing successful quark-gluon vertex interaction models with the
corresponding interaction extracted from lattice-QCD data on the quark's
propagator, we identify common qualitative features which could be important to
tune future interaction models beyond the rainbow ladder approximation.
Clearly, a quantitative comparison is conceptually not simple, but
qualitatively the results suggest that a realistic interaction should be
relatively broad with a strong support at about ~GeV and
infrared-finite
Towards flavored bound states beyond rainbows and ladders
We give a snapshot of recent progress in solving the Dyson-Schwinger equation
with a beyond rainbow-ladder ansatz for the dressed quark-gluon vertex which
includes ghost contributions. We discuss the motivations for this approach with
regard to heavy-flavored bound states and form factors and briefly describe
future steps to be taken.Comment: Contribution to the proceedings of the XXXVI Reuni\~ao de Trabalho
sobre F\'isica Nuclear no Brasil which took place in Maresias, S\~ao Paulo,
Brazil. 8 pages, 3 figures. AIP proceeding styl
Form factors in B->f0(980) and D->f0(980) transitions from dispersion relations
Within the dispersion relation approach we give the double spectral
representation for space-like and time-like B-> f_0(980) and D-> f_0(980)
transition form factors in the full q^2 range. The spectral densities, being
the input of the dispersion relations, are obtained from a triangle diagram in
the relativistic quark model.Comment: Talk given at MESON 2006, Krakow, 9-13 June 200
The Electromagnetic Form Factor of the Kaon in the Light-Front Approach
The kaon electromagnetic form factor is calculated within a light-front
constituent quark model (LFCQM). The electromagnetic components of the current
are extracted from the Feynman triangle diagram within the light-front
approach. We also obtain the electroweak decay constant and the charge radius
for the kaon in the light-front approach. In this work, the kaon observables
are calculated and a fairly good agreement is obtained with a very higher
accuracy when compared with the experimental data.Comment: Paper with 4 pages, 1 figure, reference: XII HADRON PHYSICS
Conference - to appear in AIP Conference Proceeding
Scalar meson properties from D-meson decays
Decay amplitudes of D(D_s)->f0(980)X, X=pi, K, are compared to experimental
branching ratios with the aim of singling out the poorly known D->f0(980)
transition form factor in these amplitudes. Since the other elements of the
amplitudes are either calculable in an effective QCD theory using operator
product expansion or are known from experiment (e.g. the pion and kaon decay
constants), we can take advantage of these reactions to constrain the
transition form factors obtained in relativistic quark models. In these models,
the f0(980) wavefunction requires an unknown size parameter for both its
non-strange ubar u(dbar d) and strange sbar s components, which we fit to the
D(D_s) decay data.Comment: Talk given at the Few Body 18 conference in Santos, Brazil. 4 pages,
to be published in Nuclear Physics
Electromagnetic Structure of the Pion
In this work, we analyze the electromagnetic structure of the pion. We
calculate its electromagnetic radius and electromagnetic form factor in low and
intermediate momentum range. Such observables are determined by means of a
theoretical model that takes into account the constituent quark and antiquark
of the pion within the formalism of light-front field theory. In particular, we
consider a nonsymmetrical vertex in this model, with which we calculate the
electromagnetic form factor of the pion in an optimized way, so that we obtain
a value closer to the experimental charge radius of the pion. The theoretical
calculations are also compared with the most recent experimental data involving
the pion electromagnetic form factor and the results show very good agreement.Comment: Paper with 4 pages, 1 figure, presented in XII HADRON PHYSICS
Conference - to appear in AIP Conference Proceeding
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