Low-Energy Pion Production at 0° with Heavy Ions from 125 to 400 MeV/Nucleon

The results of a systematic study of 0° pion production by heavy ions from 125 to 400 MeV/nucleon are presented. The dependence of the cross section on the mass number of the target, the energy of the beam, and the pion charge and energy are discussed. A striking feature of the data is an unexpectedly large $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratio for pions of valocity close to the projectile velocity.