Possible Production of the Sigma Meson in Nuclei

It should be a typical subject in this workshop to explore possible change of hadron properties in association with that of QCD vacuum due to an environmental change. In this report, we first summarize what hadrons are expected to show such a change and how they do. Then we propose several experiments including the ones utilizing electron and photon beams for examining possible restoration of chiral symmetry in nuclei and the possible existence of the sigma meson. The experiments are based on the observation that the sigma meson may decrease the mass and the width along with the partial restoration of chiral symmetry in the medium.