Narrow Results

The latest results from the NA48/2 collaboration on charged kaon decays will be reviewed in this paper. The high statistics available, collected during 2003 and 2004 runs, allows the study of charged kaon decays up to branching ratios (BR) of ~ 10^-8. The status of the analyses of several radiative decays (K^± → π^±π⁰γ, K^± → π^±γγ, K^± → π^±e⁺e^-γ and K^± → π^±e⁺e^-) will be discussed, including BR measurements and possible ChPT tests.

In this paper, I review the status of CP violation in hyperon decay in light of recent progress by BESIII and the anticipated improvements at the super tau-charm facility. I emphasize the complementarity between kaons and hyperons for studying CP violation in $|\mathrm{\Delta }S|=1,2$ processes.

Spin-physics projects at J-PARC are explained by including future possibilities. J-PARC is the most-intense hadron-beam facility in the high-energy region above multi-GeV, and spin physics will be investigated by using secondary beams of kaons, pions, neutrinos, muons, and antiproton as well as the primary-beam proton. In particle physics, spin topics are on muon $g-2$, muon and neutron electric dipole moments, and time-reversal violation experiment in a kaon decay. Here, we focus more on hadron-spin physics as for future projects. For example, generalized parton distributions (GPDs) could be investigated by using pion and proton beams, whereas they are studied by the virtual Compton scattering at lepton facilities. The GPDs are key quantities for determining the three-dimensional picture of hadrons and for finding the origin of the nucleon spin including partonic orbital-angular-momentum contributions. In addition, polarized parton distributions and various hadron spin topics should be possible by using the high-momentum beamline. The strangeness contribution to the nucleon spin could be also investigated in principle with the neutrino beam with a near detector facility.