Pion production and charged-particle multiplicity selection in relativistic nuclear collisions

Spectra of positive pions with energies of 15-95 MeV were measured for high energy proton, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ bombardments of targets of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{107,109}{}_{}{}^{}\mathrm{Ag}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. A Si-Ge telescope was used to identify charged pions by $\frac{\mathrm{dE}}{\mathrm{dx}}-E$ and, in addition, stopped ${\pi }^{+}$ were tagged by the subsequent muon decay. In all, results for 14 target-projectile combinations are presented to study the dependence of pion emission patterns on the bombarding energy (from $\frac{E}{A}=0.25\mathrm{} \mathrm{to} 2.1$ GeV) and on the target and the projectile masses. In addition, associated charged-particle multiplicities were measured in an 80-paddle array of plastic scintillators, and used to make impact parameter selections on the pion-inclusive data.