Low-energy pion production in high-energy nucleus-nucleus collisions

Doubly differential cross sections for production of pions with 400-MeV/N /sup 20/Ne on C, NaF, Cu, and Pb have been measured for a range of 20 MeV < T/sub ..pi..//sup LAB/ < 100 MeV and 30/sup 0/ < theta/sub ..pi..//sup LAB/ < 150/sup 0/. The results are compared with previous data with 800-MeV/N /sup 20/Ne. The broad maximum at theta/sub ..pi..//sup c.m./ = 90/sup 0/ in the center-of-mass angular distribution of low-energy pions observed at 800 MeV/N is not seen at the present energy. Neither was such a maximum at the central-rapidity region observed in (p + nucleus) reactions at E/sub p/ = 730 MeV. The 90/sup 0/ maximum seems to be a phenomenon specific to nucleus-nucleus collisions around 1 GeV/N, where the multiplicity of ..delta.. formation is high and multiple ..delta.. interaction could influence the pion production. The distribution at higher bombarding energies has yet to be studied.