144 research outputs found
Near-threshold Lambda(1520) production by the gamma p -> K+Lambda(1520) reaction at forward K+ angles
Differential cross sections and photon-beam asymmetries for the gamma p -> K+
Lambda(1520) reaction have been measured with linearly polarized photon beams
at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump
structure was found at W=2.11 GeV in the cross sections. The bump is not well
reproduced by theoretical calculations introducing a nucleon resonance with
J<=3/2. This result suggests that the bump might be produced by a nucleon
resonance possibly with J>=5/2 or by a new reaction process, for example an
interference effect with the phi photoproduction having a similar bump
structure in the cross sections.Comment: 5 pages, 4 figures, published in Phys. Rev. Let
Measurement of the Reaction at Backward Angles
Cross sections for the have been measured at
backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV.
In addition, the beam asymmetry for this reaction has been measured for the
first time at backward angles. The was detected at forward angles in
the LEPS spectrometer via its decay to and the K^+ was inferred using
the technique of missing mass. These measurements, corresponding to kaons at
far backward angles in the center-of-mass frame, complement similar CLAS data
at other angles. Comparison with theoretical models shows that the reactions in
these kinematics provide further opportunities to investigate the reaction
mechanisms of hadron dynamics.Comment: 6 figures, submitted to PRC rapid communication
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
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
The gamma + p to K+ + Lambda and gamma + p to K+ + Sigma0 reactions at forward angles with photon energies from 1.5 to 2.4 GeV
Differential cross sections and photon beam asymmetries for the gamma p
rightarrow K+ Lambda and gamma p rightarrow K+ Sigma0 reactions have been
measured in the photon energy range from 1.5 GeV to 2.4 GeV and in the angular
range from Theta_{cm} = 0 to 60 of the K+ scattering angle in the center of
mass system at the SPring-8/LEPS facility. The photon beam asymmetries for both
the reactions have been found to be positive and to increase with the photon
energy. The measured differential cross sections agree with the data measured
by the CLAS collaboration at cosTheta_{cm}<0.9 within the experimental
uncertainties, but the discrepancy with the SAPHIR data for the K+Lambda
reaction is large at cosTheta_{cm}>0.9. In the K+Lambda reaction, the
resonance-like structure found in the CLAS and SAPHIR data at W=1.96 GeV is
confirmed. The differential cross sections at forward angles suggest a strong
K-exchange contribution in the t-channel for the K+Lambda reaction, but not for
the K+Sigma0 reaction.Comment: 13 pages, 18 figures, submitted to Physical Review
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0
reactions are measured for the first time for Egamma=1.5-2.4 GeV and
0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the
Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are
positive and gradually increase with rising photon energy. The data are not
consistent with theoretical predictions based on tree-level effective
Lagrangian approaches. Including the new results in the development of the
models is, therefore, crucial for understanding the reaction mechanism and to
test the presence of baryon resonances which are predicted in quark models but
are sofar undiscovered
Differential cross section and photon beam asymmetry for the gamma n -> K+ Sigma- reaction at Egamma=1.5-2.4 GeV
Differential cross sections and photon beam asymmetries have been measured
for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately
using liquid deuterium and hydrogen targets with incident linearly polarized
photon beams of Egamma=1.5-2.4 GeV at 0.6<cosTheta<1. The cross section ratio
of sigma(K+Sigma-)/sigma(K+Sigma0), expected to be 2 on the basis of the
isospin 1/2 exchange, is found to be close to 1. For the K+Sigma- reaction,
large positive asymmetries are observed indicating the dominance of the
K*-exchange. A large difference between the asymmetries for the K+Sigma- and
K+Sigma0 reactions can not be explained by simple theoretical considerations.Comment: 5 pages, 3 figures, accepted by Phys. Rev. Let
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