Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2018 American Physical Society. Differential cross sections and photon-beam asymmetries for the γ→p→π-Δ++(1232) reaction have been measured for 0.7<cosθπc.m.<1 and Eγ=1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for 1.5<Eγ(GeV)<2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure uū quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Eγ=1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of π exchange in the t channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a dd or an ss quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.

File： 1801.07900(1).pdf

DOI： 10.1103/PhysRevLett.120.202004

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PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2018 American Physical Society. Differential cross sections and photon-beam asymmetries for the γ - p→π+n reaction have been measured for 0.6<cosθπ<1 and Eγ=1.5-2.95GeV at SPring-8/LEPS. The cross sections monotonically decrease as the photon beam energy increases for 0.6<cosθπ<0.9. However, the energy dependence of the cross sections for 0.9<cosθπ<1 and Eγ=1.5-2.2GeV (W=1.9-2.2GeV) is different, which may be due to a nucleon or Δ resonance. The present cross sections agree well with the previous cross sections measured by other groups and show forward peaking, suggesting significant t-channel contributions in this kinematical region. The asymmetries are found to be positive, which can be explained by ρ exchange in the t channel. Large positive asymmetries in the small-|t| region, where the ρ-exchange contribution becomes small, could be explained by introducing π-exchange interference with the s channel.

File： 1708.09574(2).pdf

DOI： 10.1103/PhysRevC.97.015205

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Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2018 American Physical Society. We report the measurement of the γp→K+Λ and γp→K+Σ0 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 Eγ=1.5-3.0 GeV. With increasing photon energy, the cross sections for both γp→K+Λ and γp→K+Σ0 reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at Eγ=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 Λ in the whole observed energy range. A lack of similar feature for Σ0 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.

DOI： 10.1103/PhysRevC.97.015208

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Language：Japanese   Publisher：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

The nuclear spin–lattice relaxation time (T1) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer T1 under lower magnetic field and at higher temperature. The T1 of 139La and 27Al was measured under magnetic fields of 0.5–2.5 T and at temperatures of 0.1–1.5 K and found widely distributed up to 100 h. The result suggests that the T1 can be as long as T1∼ 1 h at 0.1 K with a magnetic field of 0.1 T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer T1 are discussed.

DOI： 10.1016/j.nima.2021.165845

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

File： 17T-NMR-arXiv.pdf

DOI： 10.1063/5.0005696

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Authorship：Lead author   Language：English  

J-GLOBAL

Event date： 2021.2

Presentation type：Oral presentation (general)