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تسجيل مستخدم جديدNear-threshold photoproduction of $Lambda(1520)$ from protons and deuterons
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Photoproduction of $Lambda$(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K$^{+/0}$ angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K$^+$ angles.
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The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for $gamma p to phi p$, $gamma d to phi p n$ and $gamma d to phi d$ at forward production angles. A linearly polarized photon beam at $E_{gamma}$=1.6-2.
4 GeV was used for the production of $phi$ mesons. The natural-parity Pomeron exchange processes remains dominant nearthreshold. The unnatural-parity processes of pseudoscalar exchange is visible in the production from nucleons but is greatly reduced in the coherent production from deuterons. There is no strong $E_{gamma}$-dependence, but some dependence on momentum-transfer. A small but finite value of the spin-density matrix elements reflecting helicity-nonconserving amplitudes in the $t$-channel is observed.
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.
We report the first measurement of the differential cross section on $phi$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement wa
s carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections $frac{dsigma}{dt}$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. This experiment establishes a baseline for a future experimental search for an exotic $phi$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $phi$ mesons.
We report on the measurement of spin density matrix elements of the $Lambda(1520)$ in the photoproduction reaction $gamma prightarrow Lambda(1520)K^+$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimen
tal program in Hall D at Jefferson Lab using a linearly polarized photon beam with $E_gamma =$ 8.2-8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, $-(t-t_text{0})$. We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in $Lambda(1520)$ photoproduction.
The $phi$-$Lambda(1520)$ interference effect in the $gamma pto K^+K^-p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $phi$ and $Lambda(1520)$ production amplitudes were obtaine
d in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when $K^+K^-$ pairs are observed at forward angles, but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the $sqrt{s}=2.1$ GeV bump structure in forward differential cross sections for $phi$ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange and rescattering processes via other hyperon states.
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