727 research outputs found
K+ photoproduction at SPring-8/LEPS
A series of experiments have been carried out by using a linearly polarized
photon beam at the SPring-8/LEPS facility from December 2000 to June 2001. The
photon beam asymmetries and differential cross sections of the
p(gamma,K+)Lambda and p(gamma,K+)Sigma^0 reactions have been measured in the
photon energy range from 1.5 GeV to 2.4 GeV at forward angles, 0 deg. <
Theta_cm < 60 deg.. We report preliminary results of the photon beam
asymmetries.Comment: 4 pages, 4 figures, to be published in the Proceedings (Nuclear
Physics A) of the PANIC02, Osaka, Sept 30 - Oct 4, 200
Magnetic interaction induced by the anomaly in kaon-photoproductions
We study the role of magnetic interaction in the photoproduction of the kaon
and hyperon. We find that the inclusion of a higher order diagram induced by
the Wess-Zumio-Witten term has a significant contribution to the magnetic
amplitude, which is compatible to the observed photon asymmetry in the forward
angle region. This enables us to use the K^* coupling constants which have been
determined in a microscopic way rather than the phenomenological ones which
differ largely from the microscopic ones.Comment: 8 pages, 3 figure
Strangeness Electromagnetic Production on Nucleons and Nuclei
Isobar models for the electromagnetic production of kaons are discussed with
emphasis on the K^+ photoproduction at very small kaon angles and K^0
photoproduction on deuteron. Distorted-wave impuls approximation calculations
of the cross sections for the electroproduction of hypernuclei are presented on
the case of the ^{12}B_\Lambda production.Comment: 9 pages, 7 figures, talk presented at the 10th Int. Conference on
Hypernuclear and Strange Particle Physics, Tokai, Japan, Sept. 14 - 18, 200
Electroproduction of kaons from the proton in a Regge-plus-resonance approach
We present a Regge-plus-resonance (RPR) description of the p(e,e'K^+)Y
processes (Y=\Lambda,\Sigma^0) in the resonance region. The background
contributions to the RPR amplitude are constrained by the high-energy p(\gamma,
K^+)Y data. As a result, the number of free model parameters in the resonance
region is considerably reduced compared to typical effective-Lagrangian
approaches. We compare a selection of RPR model variants, originally
constructed to describe photoproduction, with the world electroproduction
database. The electromagnetic form factors of the intermediate N^*s and
$\Delta^*s are computed in the Bonn constituent-quark model. With this input,
we find a reasonable description of the p(e,e'K^+)Y data without adding or
readjusting any parameters. It is demonstrated that the electroproduction
response functions are extremely useful for fine-tuning both the background and
resonant contributions to the reaction dynamics.Comment: 14 pages, 7 figures; added discussion on double counting in the RPR
model; accepted for publication in Phys. Lett.
Backward-angle photoproduction of mesons on the proton at = 1.5--2.4 GeV
Differential cross sections and photon beam asymmetries for
photoproduction have been measured at = 1.5--2.4 GeV and at the
scattering angles, --1 cos --0.6. The
energy-dependent slope of differential cross sections for -channel
production has been determined. An enhancement at backward angles is found
above = 2.0 GeV. This is inferred to be due to the -channel
contribution and/or resonances. Photon beam asymmetries have been obtained for
the first time at backward angles. A strong angular dependence has been found
at 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL
Gerasimov-Drell-Hearn Sum Rule and the Discrepancy between the New CLAS and SAPHIR Data
Contribution of the K^+\Lambda channel to the Gerasimov-Drell-Hearn (GDH) sum
rule has been calculated by using the models that fit the recent SAPHIR or CLAS
differential cross section data. It is shown that the two data sets yield quite
different contributions. Contribution of this channel to the forward spin
polarizability of the proton has been also calculated. It is also shown that
the inclusion of the recent CLAS C_x and C_z data in the fitting data base does
not significantly change the result of the present calculation. Results of the
fit, however, reveal the role of the S_{11}(1650), P_{11}(1710), P_{13}(1720),
and P_{13}(1900) resonances for the description of the C_x and C_z data. A
brief discussion on the importance of these resonances is given. Measurements
of the polarized total cross section \sigma_{TT'} by the CLAS, LEPS, and MAMI
collaborations are expected to verify this finding.Comment: 15 pages, 8 figure
Baryon Resonances
In this talk I show recent results on how many excited baryon resonances
appear as systems of one meson and one baryon, or two mesons and one baryon,
with the mesons being either pseudoscalar or vectors. Connection with
experiment is made including a discussion on old predictions and recent results
for the photoproduction of the resonance, as well as the
prediction of one baryon state around 1920 MeV which might have been
seen in the reaction.Comment: Talk given at the 10th International Conference on Hypernuclear and
Strange Particle Physics, Tokai, Japan, Sptember 200
Forward coherent -meson photoproduction from deuterons near threshold
Differential cross sections and decay asymmetries for coherent -meson
photoproduction from deuterons were measured for the first time at forward
angles using linearly polarized photons at = 1.5-2.4 GeV. This
reaction offers a unique way to directly access natural-parity Pomeron dynamics
and gluon exchange at low energies. The cross sections at zero degrees increase
with increasing photon energy. The decay asymmetries demonstrate a complete
dominance of natural-parity exchange processes, showing that isovector
unnatural-parity -meson exchange is small. Nevertheless the deduced cross
sections of -mesons from nucleons contributed by isoscalar t-channel
exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio
Photoproduction of Lambda(1405) and Sigma^{0}(1385) on the proton at E_\gamma = 1.5-2.4 GeV
Differential cross sections for and reactions have been measured in the photon energy range
from 1.5 to 2.4 GeV and the angular range of for the
scattering angle in the center-of-mass system. This data is the first
measurement of the photoproduction cross section. The
lineshapes of \LamS measured in and decay modes
were different with each other, indicating a strong interference of the isospin
0 and 1 terms of the scattering amplitudes. The ratios of \LamS
production to \SigS production were measured in two photon energy ranges: near
the production threshold ( GeV) and far from it ( GeV). The observed ratio decreased in the higher photon energy
region, which may suggest different production mechanisms and internal
structures for these hyperon resonances
A new perspective on the Faddeev equations and the system from chiral dynamics and unitarity in coupled channels
We review recent work concerning the interaction and Faddeev
equations with chiral dynamics which allow us to look at the from a
different perspective and pay attention to problems that have been posed in
previous studies on the subject. We show results which provide extra
experimental evidence on the existence of two states. We then
show the findings of a recent approach to Faddeev equations using chiral
unitary dynamics, where an explicit cancellation of the two body off shell
amplitude with three body forces stemming from the same chiral Lagrangians
takes place. This removal of the unphysical off shell part of the amplitudes is
most welcome and renders the approach unambiguous, showing that only on shell
two body amplitudes need to be used. With this information in mind we use an
approximation to the Faddeev equations within the fixed center approximation to
study the system, providing answers within this approximation to
questions that have been brought before and evaluating binding energies and
widths of this three body system. As a novelty with respect to recent work on
the topic we find a bound state of the system with spin S=1, like a bound state
of -deuteron, less bound that the one of S=0, where all recent efforts
have been devoted. The width is relatively large in this case, suggesting
problems in a possible experimental observation.Comment: 18 pages, 7 figures, one misprint corrected, Nuclear Physics A in
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