K. Miwa

Photoproduction ofΛ(1405)andΣ0(1385)on the proton atEγ=1.5−2.4GeV

Differential cross sections for {gamma}p{yields}K{sup +}{lambda}(1405) and {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos({theta})<1.0 for the K{sup +} scattering angle in the center-of-mass system. This data is the first measurement of the {lambda}(1405) photoproduction cross section. The line shapes of {lambda}(1405) measured in {sigma}{sup +}{pi}{sup -} and {sigma}{sup -}{pi}{sup +} decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the {sigma}{pi} scattering amplitudes. The ratios of {lambda}(1405) production to {sigma}{sup 0}(1385) production were measured in two photon energy ranges: near the production threshold (1.5<E{sub {gamma}}<2.0 GeV) and far from it (2.0<E{sub {gamma}}<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.

Nuclear-matter modification of decay widths in the phi-->e+e- and phi-->K+K- channels.

The invariant mass spectra of phi-->K+K- are measured in 12 GeV p+A reactions in order to search for the in-medium modification of phi mesons. The observed K+K- spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three betagamma regions between 1.0 and 3.5. The nuclear mass number dependence of the yields of the K+K- decay channel is compared to the simultaneously measured e+e- decay channel for carbon and copper targets. We parameterize the production yields as sigma(A)=sigma0Aalpha and obtain alphaphi-->K+K- -alphaphi-->e+e- to be 0.14+/-0.12. Limits are obtained for the partial decay widths of the phi mesons in nuclear matter.

Search for the Θ+ via the K+p→π+X reaction with a 1.2 GeV/c K+ beam

The Θ + was searched for via the K + p 2→π + X reaction using the 1.2 GeV/c K+ beam at the K6 beam line of the KEK-PS 12 GeV Proton Synchrotron. In the missing mass spectrum of the K + p p→π + X reaction, no clear peak structure was observed. Therefore a 90% C.L. upper limit of 3.5 μb/sr was derived for the differential cross section averaged over 2° to 22° in the laboratory frame of the K + p → π + Θ + reaction. This upper limit is much smaller than the theoretical calculation for the t-channel process where a K 0 * is exchanged. From the present result, either the t-channel process is excluded or the coupling constant of gK*NΘ is quite small.

Search For A Ξ Bound State In The 12C(K-,K+)X Reaction At 1.8 Gev/c

We have carried out a pilot data taking of the J-PARC E05 experiment to search for the bound state peaks of

Precise determination of

^{12}_\Xi

^{12}_{\Lambda}

Be in the

C level structure by

^{12}

\gamma

C

-ray spectroscopy

(K^-, K^+)X

High Precision γ-ray Spectroscopy of \(_\Lambda ^4\textHe\) and \(_\Lambda ^19\textF\) at J-PARC

reaction at 1.8 GeV/