33 research outputs found
Exclusive electroproduction of J/psi mesons
A nonperturbative calculation of elastic electroproduction of the J/psi meson
is presented and compared to the experimental data.
Our model describes well the observed dependences of the cross sections on
the photon virtuality Q2 and on the energy, and the measured ratio R of
longitudinal to transverse cross sections.Comment: Five *.eps figure
Nonperturbative QCD treatment of photoproduction
We present a nonperturbative QCD calculation of elastic meson
production in photon-proton scattering at high energies. Using light cone wave
functions of the photon and vector mesons, and the framework of the model of
the stochastic QCD vacuum, we calculate the differential and integrated elastic
cross sections for \gamma p \goto J/\psi p . With an energy dependence
following the two-pomeron model we are able to give a consistent description of
the integrated cross sections and the differential cross sections at low
in the range from 20 GeV up to the highest HERA energies. We discuss different
approaches to introduce saturation and find no specific effects up to energies
presently available. We also calculate and compare to experiments the cross
section for photoproduction.Comment: 24 pages, 10 figures, 4 table
Universality in the Electroproduction of Vector Mesons
We study universality in the electroproduction of vector mesons using a
unified nonperturbative approach which has already proved to reproduce
extremely well the available experimental data. In this framework, after the
extraction of factors that are specific of each vector meson, we arrive at a
reduced integrated elastic cross section which is universal. Our calculations
suggest a finite infrared behavior for the strong coupling constant.Comment: 22 pages, 10 figure
Eikonal profile functions and amplitudes for and scattering
The eikonal profile function obtained from the Model of the Stochastic
Vacuum is parametrized in a form suitable for comparison with experiment. The
amplitude and the extended profile function (including imaginary and real
parts) are determined directly from the complete pp and p elastic
scattering data at high energies. Full and accurate representation of the data
is presented, with smooth energy dependence of all parameters. The changes
needed in the original profile function required for description of scattering
beyond the forward direction are described.Comment: Latex, 28 pages and 16 figure
Hadronic sizes and observables in high-energy scattering
The functional dependence of the high-energy observables of total cross
section and slope parameter on the sizes of the colliding hadrons predicted by
the model of the stochastic vacuum and the corresponding relations used in the
geometric model of Povh and H\"ufner are confronted with the experimental data.
The existence of a universal term in the expression for the slope, due purely
to vacuum effects, independent of the energy and of the particular hadronic
system, is investigated. Accounting for the two independent correlation
functions of the QCD vacuum, we improve the simple and consistent description
given by the model of the stochastic vacuum to the high-energy pp and pbar-p
data, with a new determination of parameters of non-perturbative QCD. The
increase of the hadronic radii with the energy accounts for the energy
dependence of the observables.Comment: Latex, using Revtex.style . 2 ps figures. To be published in Physical
Review D , July 199
Nonperturbative and perturbative aspects of photo- and electroproduction of vector mesons
We discuss various aspects of vector meson production, first analysing the
interplay between perturbative and nonperturbative aspects of the QCD
calculation. Using a general method adapted to incorporate both perturbative
and nonpertubative aspects, we show that nonperturbative effects are important
for all experimentally available values of the photon virtuality Q2. We compare
the huge amount of experimental information now available with our theoretical
results obtained using a specific nonperturbative model without free
parameters, showing that quite simple features are able to explain the data.Comment: 19 page
Semileptonic D decay into scalar mesons: a QCD sum rule approach
Semileptonic decays of D-mesons into scalar hadronic states are investigated.
Two extreme cases are considered: a) the meson decays directly into an
uncorrelated scalar state of two two mesons and b) the decay proceeds via
resonance formation. QCD sum rules including instanton contributions are used
to calculate total and differential decay rates under the two assumptions.Comment: 18 pages, 9 figures, e-mail: [email protected]