Precise spectroscopic study on π meson atoms at RIKEN

In recent years, the authors have been conducting spectroscopic experiments of π meson atoms at RIKEN. The π meson atoms are the system in which π mesons are bound to atomic orbitals instead of electrons. The authors aim to measure this binding energy and width with an unprecedented accuracy using the high-intensity beams that reach several hundred pnA at RIKEN's RI Beam Factory. As the first step in 2010, the authors conducted a pilot experiment. As a result, they succeeded in the determination of binding energy via measurement for only 15 hours with a statistical accuracy comparable to the previous researches, and measured the angle dependence of reaction generation cross-sectional area for the first time in the world. This paper explains the experiments including these results. (A.O.)