Since the wave-length of a few GeV gamma-ray is less than the size of a hadron, typically a proton (~1 fm), it becomes possible to investigate its sub-structure, i.e., the world of quarks and gluons with GeV photons. A polarized GeV-photon beam with good qualities is produced by the backward-Compton scattering of laser photons from high energy electrons. Our group study the interactions and structures of hadrons in terms of the quarks and their interactions, which is called the Quark-Nuclear Physics. The experiment is performed at SPring-8 which is the synchrotron radiation ring with the highest energy (8 GeV) in the world. R&D for new experiments with high intensity hadron beams such as kaon beams at J-PARC is also in progress.
Our group has found an evidence for an exotic baryon with an anti-strange quark (penta-quark 'Theta') for the first time. Making sure of its existence and revealing its structure are two of the main goals. The investigations of the quark confinement, the partial restoration of the chiral symmetry in the nuclear medium, the freedom of quarks and gluons in the nuclear force, etc. are other objectives. The experimental study is being done with state-of-the-art technologies in order to understand the physical material from the quark-gluon level, also expecting the encounter with unknown phenomena.