Coherent, semicoherent and incoherent pion production in heavy-ion reactions

Two types of coherent pion production in heavy-ion collisions are studied and calculations are performed for 12C against 12C collisions. The first one, doubly coherent production, produces a pion in one nucleus leaving it in its ground state, while the second nucleus is excited to the 1+, T=1 state. The second process, semicoherent production, also leaves in its ground state the nucleus where the pion is produced while the second one is broken. The cross sections for forward pions are compared to the standard incoherent production process. We observe that at energies below 130 MeV/A the semicoherent process dominates the cross section for forward pion angles while at large energies around 800 MeV/A it represents a fraction of around 30% of the incoherent cross section. The doubly coherent process leads to smaller cross sections, still in the measurable range for energies above 200 MeV/A. (orig.)