Pion-transfer reaction spectroscopy of inverse kinematics for studies of deeply bound pionic atoms in heavy nuclei

Abstract

A new type of nuclear reaction spectroscopy using inverse kinematics is proposed and discussed with a special emphasis on the application to charge-exchange pion-transfer reactions such as (d, 2He) and (t, 3He) to embed real pions onto heavy nuclei forming deeply bound pionic atoms, which were predicted by Toki and Yamazaki to have narrow widths due to the repulsive strong-interaction potential. A typical case considered is to use heavy-ion projectiles of 400 MeV/u range on a light target such as d or t and to measure the recoil particles of low-energy range corresponding to forward scattering. The recoil momentum is shown to be nearly equal to the Lorentz-invariant momentum transfer of the reaction, typically, around 140 MeV/ c, which is proportional to the excitation energy. Compared to the conventional method, the present inverse-kinematics one not only provides a better energy resolution (around 100 keV at 140 MeV excitation) but also permits studies of π − bound states on unstable nuclei, hitherto unconceivable objects for spectroscopy. Some experimental configurations to be used in a cooled circulating beam are discussed.