First observation of the Δ resonance in relativistic heavy-ion charge-exchange reactions

Excitation of the Δ resonance is observed for the first time with heavy ions. It is very strong in the two mirror charge-exchange reactions (²⁰Ne, ²⁰F) and (²⁰Ne, ²⁰Na) at 950 MeV per nucleon. With similar incident energies per nucleon, the Δ is weakly excited with a ¹⁴N beam and nearly absent with a ¹²C beam. The role of the ejectile bound states is discussed.