Masses and spins of hadrons are fundamental quantities in physics; however, their origins are not well understood, and their investigation is one of the major purposes of building electron-ion colliders (EICs) in the 2030’s. Both quantities can be investigated by generalized parton distributions (GPDs). In this seminar, I explain various experimental processes for measuring the GPDs and experimental possibilities at KEK. So far, the GPDs have been investigated mainly by the deeply virtual Compton scattering and deeply virtual meson production processes at charged-lepton accelerator facilities. They could be investigated by high-energy neutrino facilities in the future.

At KEK, it is possible to investigate the GPDs using the e^+ e^- collider KEKB and the hadron-accelerator facility J-PARC. We can extract the s-channel GPDs and gravitational form factors of hadrons by the two-photon processes gamma^* + gamma -> h + h-bar, where h is a hadron. Actually, there was the first report on the determination of gravitational form factors and radii from KEKB measurements in 2018. At J-PARC, the GPDs will be investigated by the exclusive Drell-Yan process pi^- p -> mu^+ mu^- B, where the baryon B could be a nucleon or Delta. In the future, other processes could be studied for the GPDs. For example, the 2->3 reaction processes NN -> N pi B could be used for probing the GPDs in the ERBL (Efremov-Radyushkin-Brodsky-Lepage) region.