72 research outputs found
Study of the threshold behavior of the N scattering amplitude through the associated photoproduction of - and -mesons
We suggest that the reaction cross section, in the
kinematics where the invariant mass in the final state lies between
the threshold value (m+m) and the N*(1535) resonance mass, is
largely determined by the scattering amplitude close to threshold. The
initial photon energy is chosen in the range GeV, in
order to reach low (absolute) values of the squared 4-momentum transfer from
the initial photon to the final -meson. In these conditions, we expect
the t-channel - and -meson exchanges to drive the dynamics
underlying the process. We show that the
-exchange is the dominating contribution to the cross section while the
-exchange is negligible. The - interference is of the order
of . The sign of this term is not known and alters significantly our
results. Data on the process would be therefore very
useful to help unravelling the behavior of the scattering amplitude
close to threshold and assessing the possibility of producing -nucleus
bound states.Comment: 8 pages, 6 figures, Invited talk at MESON 2006, June 9th-13th, 2006,
Cracow (Poland
e+e- pair production from nucleon targets in the resonance region
We present consistent theoretical descriptions of the
and reactions on proton and neutron targets for total
center of mass energies ranging between 1.50 GeV and 1.75 GeV. These
reactions are complementary to study the coupling of low-lying baryon
resonances to vector meson-nucleon channels. We show in particular how the
resonant structure of the amplitudes for both processes generates specific and
large quantum interferences between - and -meson decays into
pairs. Data on the and
reactions are expected in the near future from the HADES program at GSI and
from dilepton studies with CLAS at JLab.Comment: 6 pages, 6 figures, Paper presented at Hirschegg 2004, 'Probing
nuclei and nucleons with electrons and photons', January 12th-16th, 200
Dynamics of strong and radiative decays of Ds-mesons in the hadrogenesis conjecture
The positive parity scalar D(2317) and axial-vector D(2460)
charmed strange mesons are generated by coupled-channel dynamics through the
s-wave scattering of Goldstone bosons off the pseudoscalar and vector
D(D)-meson ground states. The specific masses of these states are obtained
as a consequence of the attraction arising from the Weinberg-Tomozawa
interaction in the chiral Lagrangian. Chiral corrections to order Q
are calculated and found to be small. The D(2317) and D(2460)
mesons decay either strongly into the isospin-violating D and
D channels or electromagnetically. We show that the -
and (KD-KD) mixings act constructively to generate strong
widths of the order of 140 keV and emphasize the sensitivity of this value to
the component of the states. The one-loop contribution to the radiative
decay amplitudes of scalar and axial-vector states is calculated using the
electromagnetic Lagrangian to chiral order Q. We show the importance
of taking into account processes involving light vector mesons explicitly in
the dynamics of electromagnetic decays. The radiative width are sensitive to
both and components, hence providing information complementary
to the strong widths on the positive parity -meson structure.Comment: 4 pages, Invited Contribution to QNP09, Beijing, September 21-26,
200
Dynamics of strong and radiative decays of Ds mesons
The positive parity scalar D(2317) and axial-vector D(2460)
charmed strange mesons are generated by coupled-channel dynamics through the
s-wave scattering of Goldstone bosons off the pseudoscalar and vector
D(D)-meson ground states. The attraction leading to the specific masses of
these states reflects the chiral symmetry breaking scale which characterizes
the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections
to order Q are calculated and found to be small. The D(2317)
and D(2460) mesons decay either strongly into the isospin-violating
D and D channels or electromagnetically. We show that
the - and (KD-KD) mixings act constructively to
generate strong widths of the order of 140 keV. The one-loop contribution to
the radiative decay amplitudes of scalar and axial-vector states is calculated
using the electromagnetic Lagrangian to chiral order Q. We show the
importance of taking into account processes involving light vector mesons
explicitly in the dynamics of electromagnetic decays to obtain a satisfactory
description of the available data.Comment: Contribution to the Meson 2008 Conference, June 6-10, Cracow, Polan
The reaction close to the vector meson production threshold
The and reaction cross sections
are calculated below and in the vicinity of the vector meson (,
) production threshold. These processes are largely responsible for the
emission of pairs in pion-nucleus reactions and contribute to the
dilepton spectra observed in relativistic heavy ion collisions. They are
dominated by the decay of low-lying baryon resonances into vector meson-nucleon
channels. The vector mesons materialize subsequently into pairs. Using
and amplitudes calculated in the
center of mass energy interval GeV, we compute the and reaction cross sections in these
kinematics. Below the vector meson production threshold, the
interference in the channel appears largely destructive for the
cross section and constructive for the cross section. The pion beam and the HADES detector at GSI offer a unique
possibility to measure these effects. Such data would provide strong
constraints on the coupling of vector meson-nucleon channels to low-lying
baryon resonances.Comment: Talk given at the Budapest'02 Workshop on Quark and Hadron Dynamics,
Budapest (Hungary), March 3rd-7th, 200
The two pion decay of the Roper resonance
We evaluate the two pion decay of the Roper resonance in a model where
explicit re-scattering of the two final pions is accounted for by the use of
unitarized chiral perturbation theory. Our model does not include an explicit
or scalar-isoscalar meson decay mode, instead it
generates it dynamically by means of the pion re-scattering. The two ways,
explicit or dynamically generated, of introducing this decay channel have very
different amplitudes.
Nevertheless, through interference with the other terms of the model we are
able to reproduce the same phenomenology as models with explicit consideration
of the meson.Comment: 17 latex pages, 11 eps figures. A few misprints corrected. A few new
references. Version accepted for publication in Phys. Rev.
Eta meson production in nucleon-nucleon collisions within an effective Lagrangian model
We investigate the pp --> pp eta and pn --> pn eta reactions within an
effective Lagrangian model for laboratory kinetic energies ranging from very
close to eta meson production threshold to about 10 GeV. Production amplitudes
include contributions from the mechanism of excitation, propagation and decay
of N*(1535), N*(1650), and N*(1710) baryonic resonances. The initial
interaction between two incoming nucleons is modeled by the exchange of pi,
rho, omega and sigma mesons where the vertex parameters are taken to be the
same as those used in the previous applications of this model. Parameters of
the resonance vertices also have been taken from our earlier studies wherever
applicable. Calculations have been done for total as well as differential eta
production cross sections. To describe the data for energies closer to the
production threshold final state interactions among the out-going particles
have been included by means of a generalized Watson-Migdal method. Terms
corresponding to the excitation of N*(1535) resonance and pion exchange process
dominate the cross sections. With a single set of vertex parameters our model
is able to describe the available data well on total cross sections for beam
energies ranging from close to threshold to upto 10 GeV.Comment: 33 pages, 11 figures, one new appendix added, discussions extende
The decay and the coupling constant g
The experimental branching ratio for the radiative decay
is used to estimate the coupling constant
for a set of values of -meson parameters
M and . Our results are quite different than the
values of this constant used in the literature.Comment: 9 pages(RevTex), 5 ps figure
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