699 research outputs found
Improved Fixed Center Approximation of the Faddeev equations for the system with S=0
We extend the Fixed Center Approximation (FCA) to the Faddeev Equations for
the system with S=0, including the charge exchange mechanisms in
the rescattering which have been ignored in former works within the
FCA. We obtain similar results to those found before, but the binding is
reduced by 6 MeV. At the same time we also evaluate the explicit contribution
the intermediate state in the three body system and find that it
produces and additional small decrease in the binding of about 3 MeV. The
system appears bound by about 35 MeV and the width omitting two body
absorption, is about 50 MeV.Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1102.285
at finite density
We study the decay channels of the in a nuclear medium and
find a sizable change - of the order of factor five - of the width of this
hyperon at normal nuclear matter density. The mass shift of the
is moderate.Comment: Presented at Particles and Nuclei International Conference (PANIC
05), Santa Fe, New Mexico, 24-28 Oct 200
dependence of the - and -induced production of the from nuclei
Using results of a recent calculation of the in the nuclear
medium, which show that the medium width is about five times the free width, we
study the A dependence of the production cross section in the
reactions and . We find a sizable A dependence in the ratio of the
nuclear cross sections for heavy nuclei with respect to a light one due to the
large value of the width in the medium, showing that devoted
experiments, easily within reach in present facilities, can provide good
information on that magnitude by measuring the cross sections studied here.Comment: 14 pages, 5 figure
Chiral dynamics in the gamma p --> pi^0 eta p and gamma p --> pi^0 K^0 Sigma^+ reactions
Using a chiral unitary approach for meson-baryon scattering in the
strangeness zero sector, where the resonance is dynamically
generated, we study the reactions and at photon energies at which the final states are produced
close to threshold. Among several reaction mechanisms, we find the most
important is the excitation of the state which subsequently
decays into a pseudoscalar meson and a baryon belonging to the
decuplet. Hence, the reaction provides useful information with which to test
current theories of the dynamical generation of the low-lying states.
The first reaction is shown to lead to sizable cross sections and the
resonance shape is seen clearly in the invariant mass
distribution. The same dynamical model is shown to lead to much smaller cross
sections at low energies in the second reaction. Predictions are made for cross
sections and invariant mass distributions which can be compared with
forthcoming experiments at ELSA.Comment: 22 pages, 22 figure
Study of and interactions in and relationship to the , states
We use the local hidden gauge approach in order to study the and
interactions for isospin I=1. We show that both interactions via
one light meson exchange are not allowed by OZI rule and, for that reason, we
calculate the contributions due to the exchange of two pions, interacting and
noninteracting among themselves, and also due to the heavy vector mesons. Then,
to compare all these contributions, we use the potential related to the heavy
vector exchange as an effective potential corrected by a factor which takes
into account the contribution of the others light mesons exchange. In order to
look for poles, this effective potential is used as the kernel of the
Bethe-Salpeter equation. As a result, for the interaction we find
a loosely bound state with mass in the range MeV, very close to
the experimental value of the reported by Belle Collaboration. For
the case, we find a cusp at MeV for all spin
cases.Comment: 23 pages, 20 figure
\phi K^{+}K^{-} production in electron-positron annihilation
In this work we study the e^{+}e^{-}\to\phi K^{+}K^{-} reaction. The leading
order electromagnetic contributions to this process involve the \gamma*\phi\
K^{+}K^{-} vertex function with a highly virtual photon. We calculate this
function at low energies using R\chi PT supplemented with the anomalous term
for the VV'P interactions. Tree level contributions involve the kaon form
factors and the K*K transition form factors. We improve this result, valid for
low photon virtualities, replacing the lowest order terms in the kaon form
factors and K*K transition form factors by the form factors as obtained in
U\chi PT in the former case and the ones extracted from recent data on
e^{+}e^{-}\to KK* in the latter case. We calculate rescattering effects which
involve meson-meson amplitudes. The corresponding result is improved using the
unitarized meson-meson amplitudes containing the scalar poles instead of the
lowest order terms. Using the BABAR value for BR(X\to \phi f_{0})\Gamma (X\to
e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good
description of data is obtained in the case of destructive interference between
this contribution and the previous ones, but more accurate data on the
isovector K*K transition form factor is required in order to exclude
contributions from an intermediate isovector resonance to e^{+}e^{-}\to \phi\
K^{+}K^{-} around 2.2 GeV.Comment: 21 pages, 17 figures. Revised version to appear in Phys. Rev. D.
Contributions of intermediate X(2175) included. Extraction of form factors
update
Baryonic Resonances from the Interactions of the Baryon Decuplet and Meson Octet
We study -wave interactions of the baryon decuplet with the octet of
pseudoscalar mesons using the lowest order chiral Lagrangian. We find two bound
states in the SU(3) limit corresponding to the octet and decuplet
representations. These are found to split into eight different trajectories in
the complex plane when the SU(3) symmetry is broken gradually. Finally, we are
able to provide a reasonable description for a good number of 4-star
resonances listed by the Particle Data Group. In particular, the
, the and the states are well
reproduced. We predict a few other resonances and also evaluate the couplings
of the observed resonances to the various channels from the residues at the
poles of the scattering matrix from where partial decay widths into different
channels can be evaluated.Comment: Contribution to the HADRON05 Conference, Rio de Janeiro, September
200
and in the nuclear medium
Recent studies of the resonance within chiral unitary theory
with coupled channels find the resonance as a dynamically generated state from
the interaction of the decuplet of baryons and the octet of mesons, essentially
a quasibound state of in this case, although the coupling
of the to the and makes this picture
only approximate. The decay channel of the
is forbidden in free space for the nominal mass of the , but
the coupling of the to components in the nuclear medium opens new
decay channels of the in the nucleus and produces a much larger
width. Together with medium modifications of the and
decay channels, the final width of the at nuclear matter
density is more than five times bigger than the free one. We perform the
calculations by dressing simultaneously the and the
resonances, finding moderate changes in the mass but
substantial ones in the width of both resonances.Comment: 20 pages, 6 figures; comparison made to data, new references and new
(small) decay channel include
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