High‐energy hadron physics at J‐PARC

The J‐PARC facility is near completion and experiments will start in 2009 on nuclear and particle physics projects. In this article, the J‐PARC facility is introduced, and possible projects are discussed in high‐energy hadron physics by using the primary proton beam of 30–50 GeV. There are proposed experiments on charm‐production and Drell‐Yan processes as well as single spin asymmetries for investigating quark and gluon structure of the nucleon and nuclei. Parton‐energy loss could be studied in the Drell‐Yan processes. There is also a proposal on hadron‐mass modifications in a nuclear medium by using the proton beam. In addition, possible topics include transition from hadron to quark degrees of freedom by elastic $pp$ scattering, color transparency by $(p,2p),$ short‐range correlation in nuclear force by $(p,2pN),$ tensor structure functions for spin‐one hadrons, fragmentation functions, and generalized partem distributions in the ERBL region although proposals are not written on these projects. If proton‐beam polarization is attained, it is possible to investigate details of nucleon spin structure. In the last part of this article, our own studies are explained on partem distribution functions in connection with the J‐PARC projects.