Production of the pionic atom in heavy-ion collisions

Abstract

We estimate the production cross section of negative pions from the target in heavy-ion reactions into the atomic orbits of the projectile's Coulomb field. The cross section is appreciable for high-energy heavy-ion collisions with heavy projectiles and targets. It favors production of pions in the lower atomic orbits with the target nucleus excited collectively. We argue that it is very likely that these pions will be ionized by the target's Coulomb field, leading to a peak of the π − spectrum near the projectile velocity. For those pions which remain in the orbits, correlation measurements of the pionic X-rays and the projectile residue could also signal the existence of the process. We point out that both the pion condensate mode and the isovector magnetic dipole mode of the target nucleus could be excited via this process. This investigation, therefore, offers interesting possibilities for studying these excitations.