1,747 research outputs found
On the possibility of observation in low energy collisions
Within the meson-exchange model we calculate -meson production cross
section in \piN and reactions and investigate the possibility for
observation via the decay mode in collisions. Our studies
indicate that an extraction of the signal is unlikely due to the large
background from other reaction channels.Comment: 6 pages, LaTeX, including 10 postscript figures, to appear in Eur.
Phys. J.
Density dependence of resonance broadening and shadowing effects in nuclear photoabsorption
Medium effects as a function of the mass number are studied in the total
photonuclear cross section from the -resonance region up to the region
where shadowing effects are known to exist. A consistent picture is obtained by
simply assuming a density dependence of the different mechanisms of resonance
broadening and shadowing. The -mass shift is found to increase with
.Comment: 7 pages, LaTeX, 2 figures available from the author
Production of -mesons in the reactions and at GeV energies
We investigate the reactions and near
threshold and at medium energies. An effective Lagragian approach and the Regge
pole model are applied to analyze different contributions to the cross section
of the reaction . These results are used to calculate the
differential and total cross sections of the reaction within
the framework of the two-step model in which two nucleons produce an
-meson via -meson exchange and fuse to a deuteron. The necessity of
new measurements on production and branching fractions (of its decay to
the and channels) is emphasized for clarifying the
structure. Detailed predictions for the reaction are presented
for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure
Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory
The mean field (MF) approximation for the pion matter, being equivalent to
the leading ChPT order, involves no dynamical loops and, if self-consistent,
produces finite renormalizations only. The weight factor of the Haar measure of
the pion fields, entering the path integral, generates an effective Lagrangian
which is generally singular in the continuum limit.
There exists one parameterization of the pion fields only, for which the weight
factor is equal to unity and , respectively. This
unique parameterization ensures selfconsistency of the MF approximation. We use
it to calculate thermal Green functions of the pion gas in the MF approximation
as a power series over the temperature. The Borel transforms of thermal
averages of a function of the pion
fields with respect to the scalar pion density are found to be
. The perturbation series over the scalar
pion density for basic characteristics of the pion matter such as the pion
propagator, the pion optical potential, the scalar quark condensate
, the in-medium pion decay constant , and the
equation of state of pion matter appear to be asymptotic ones. These series are
summed up using the contour-improved Borel resummation method. The quark scalar
condensate decreases smoothly until MeV. The temperature
is the maximum temperature admissible for thermalized non-linear
sigma model at zero pion chemical potentials. The estimate of is
above the chemical freeze-out temperature MeV at RHIC and above
the phase transition to two-flavor quark matter MeV,
predicted by lattice gauge theories.Comment: Replaced with revised and extended version. Results are compared to
lattice gauge theories. 16 pages REVTeX, 13 eps figure
Low-lying Pentaquark states in the Inherent Nodal Structure Analysis
The strangeness pentaquark states as clusters are
investigated in this letter. Starting from the inherent geometric symmetry, we
analyzed the inherent nodal structure of the system. As the nodeless states,
the low-lying states are picked out. Then the S-wave state and P-wave state may be the
candidates of low-lying pentaquark states. By comparing the accessibility of
the two states and referring the presently obtained K-N interaction potential,
we propose that the quantum numbers of the observed pentaquark state
may be and L=1.Comment: 15 pages, 2 figures, 4 tables. Revised version with detailed
description, expanded discussion and reference for the geometric
configuration to be proposed being adde
Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories
We investigate deuteron two-body photodisintegration within the framework of
the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special
attention is paid to the use of QCD motivated Regge trajectories of the
logarithmic and square-root form which have been suggested recently by
Brisudov\'{a}, Burakovsky and Goldman. We find that the recent experimental
data from TJNAF in the few GeV region can reasonably be described by the model.
Angular distributions at different -energies are presented and the
effect of a forward-backward asymmetry is discussed. Predictions for the energy
dependence of at higher energies and different are
presented, too.Comment: 21 pages, LaTeX, including 6 postscript figures; submitted to Phys.
Rev.
Comparing phenomenological recipes with a microscopic model for the electric amplitude in strangeness photoproduction
Corrections to the Born approximation in photo-induced strangeness production
off a proton are calculated in a semi-realistic microscopic model. The vertex
corrections and internal contributions to the amplitude of the reaction are included on the one-loop level. Different
gauge-invariant phenomenological prescriptions for the modification of the Born
contribution via the introduction of form factors and contact terms are
discussed. In particular, it is shown that the popular minimal-substitution
method of Ohta corresponds to a special limit of the more realistic approach.Comment: 10 pages, 6 figures in the tex
Compton scattering on the nucleon at intermediate energies and polarizabilities in a microscopic model
A microscopic calculation of Compton scattering on the nucleon is presented
which encompasses the lowest energies -- yielding nucleon polarizabilities --
and extends to energies of the order of 600 MeV. We have used the covariant
"Dressed K-Matrix Model" obeying the symmetry properties which are appropriate
in the different energy regimes. In particular, crossing symmetry, gauge
invariance and unitarity are satisfied. The extent of violation of analyticity
(causality) is used as an expansion parameter.Comment: 35 pages, 15 figures, using REVTeX. Modified version to be published
in Phys. Rev. C, more extensive comparison with data for Compton scattering,
all results unchange
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