J-PARC hadron physics and future possibilities on color transparency

The J-PARC is a hadron-accelerator facility to provide secondary beams of kaons, pions, neutrinos, muons, and the others together with the primary proton beam for investigating a wide range of science projects. High-energy hadron physics can be studied by using high-momentum beams of unseparated hadrons, which are essentially pions, and also primary protons. In this report, possible experiments are explained on color transparency and generalized parton distributions (GPDs). These projects are complementary to lepton-scattering experiments at JLab, COMPASS/AMBER, and future electron-ion colliders. Because of hadron-beam energies up to 30 GeV, the J-PARC is a unique facility to investigate the transition region from the hadron degrees of freedom to the quark-gluon one. It is suitable for finding mechanisms of the color transparency. Such color-transparency studies are also valuable for clarifying factorization of hadron-production processes in extracting the GPDs from actual measurements. These studies will lead to the understanding of basic high-energy hadron interactions in nuclear medium and to clarifications on the origins of hadron spins, masses, and internal pressure mechanisms.