Speaker
Description
Due to the non-perturbative nature of QCD in the present low temperature universe, the vacuum has hidden underlying structures. We are making experimental studies to study the structure through precision spectroscopy of meson-nucleus bound systems. Recently we reported the first quantitative evaluation of the chiral condensate in the nuclear matter observed in the spectroscopy of pionic atoms. Also, there are experiments to search for eta'-mesic nuclei, which may serve information on the axial U(1) anomaly. We will discuss the achievements and the present status of these experimental challenges together with the future perspectives.