A laser-Compton backscattering beam, which we call a `Laser-Electron Photon beam, was upgraded at the LEPS beamline of SPring-8. We accomplished the gains in backscattered photon beam intensities by factors of 1.5--1.8 with the injection of two adjac
ent laser beams or a higher power laser beam into the storage ring. The maximum energy of the photon beam was also extended from 2.4 GeV to 2.9 GeV with deep-ultraviolet lasers. The upgraded beams have been utilized for hadron photoproduction experiments at the LEPS beamline. Based on the developed methods, we plan the simultaneous injection of four high power laser beams at the LEPS2 beamline, which has been newly constructed at SPring-8. As a simulation result, we expect an order of magnitude higher intensities close to 10$^7$ sec$^{-1}$ and 10$^6$ sec$^{-1}$ for tagged photons up to 2.4 GeV and 2.9 GeV, respectively.
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 d
euterium 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.
The gamma d to K^+K^-pn reaction has been studied to search for the evidence of the Theta^+ by detecting K^+K^- pairs at forward angles. The Fermi-motion corrected nK^+ invariant mass distribution shows a narrow peak at 1.524 +- 0.002 + 0.003 GeV/c^2
. The statistical significance of the peak calculated from a shape analysis is 5.1 sigma, and the differential cross-section for the gamma n to K^- Theta^+ reaction is estimated to be 12 +- 2 nb/sr in the photon energy range from 2.0 GeV to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the Theta^+ in the gamma n center-of-mass system. The obtained results support the existence of the Theta^+.
