Search

We have carried out exclusive measurements for the photoproduction of an $η$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $γp \to ηp$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0 < \cos{θ^η_{\mathrm{c.m.}}} < 0.6$. The reaction is identified by selecting a proton and two $γ$'s produced by an $η$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $η$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $η$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies., 16 pages, 11 figures

Differential cross sections and photon-beam asymmetries for the gamma p -> pi- Delta++(1232) reaction have been measured for 0.7, Accepted by Phys. Rev. Lett., 5 pages, 4 figures

We report the measurement of the $��p \rightarrow K^{+}��$ and $��p \rightarrow K^{+}��^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_��=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $��p \rightarrow K^{+}��$ and $��p \rightarrow K^{+}��^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_��=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $��$ in the whole observed energy range. A lack of similar feature for $��^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime., published version, two-column format, 10 pages, 8 figures

Differential cross sections and photon beam asymmetries for the gamma p -> pi+ n reaction have been measured for 0.6, Accepted by Phys. Rev. C

The $��$-$��(1520)$ interference effect in the $��p\to K^+K^-p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $��$ and $��(1520)$ production amplitudes were obtained 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 $��$ 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.

We report the measurement of differential cross sections for $��$ and $��'$ photoproduction from protons at backward angles ($-1.02.4$ GeV. A bump structure in the $\sqrt{s}$ dependence of the differential cross sections for $��'$ mesons was observed at $\sqrt{s}\sim$2.35 GeV., 15pages 4figures

Coherent photonuclear isotope transmutation (CPIT) produces exclusively radioactive isotopes (RIs) by coherent photonuclear reactions via E1 giant resonances. Photons to be used are medium energy photons produced by laser photons backscattered off GeV electrons. The cross sections are as large as 0.2 - 0.6 b, being independent of individual nuclides. A large fraction of photons is effectively used for the photonuclear reactions, while the scattered GeV electrons remain in the storage ring to be re-used. CPIT with medium energy photons provides specific/desired RIs with the high rate and the high density for nuclear science, molecular biology and for nuclear medicines., Comment: 8 pages, 2 figures

Differential cross sections for eta photoproduction off protons have been measured at E_gamma = 1.6 - 2.4 GeV in the backward direction. A bump structure has been observed above 2.0 GeV in the total energy. No such bump is observed in cross sections for eta', omega and pi0 photoproductions. It is inferred that this unique structure in eta photoproduction is due to a baryon resonance with a large portion of ss-bar strongly coupled to the etaN channel., Comment: 3 figures, Submitted to PRL

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=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., 5 pages, 4 figures, published in Phys. Rev. Lett

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 $E_��$= 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., 14 pages, 6 figures. Final published version

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, 5 pages, 3 figures, accepted by Phys. Rev. Lett

Photoproduction of $��$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_��$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_��$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $��$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes., 6 pages, error on the cross sections were corrected, accepted for publication in Phys. Rev. Lett

We show that the cross sections of the $��^+$-pentaquark production in different processes decrease with energy faster than the cross sections of production of the conventional three-quark hyperons. Therefore, the threshold region with the initial energy of a few GeV or less seemsto be more favorable for the production and experimental study of $��^+$-pentaquark., 4 pages, 4 figures

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