Pion Production in theAr40+Ca40Reaction at 1.05 GeV/Nucleon

Pion-production cross sections have been measured for the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}+{}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}\to {\pi }^{+}+X$ at a laboratory energy of 1.05 GeV/nucleon. A maximum in the ${\pi }^{+}$ cross section occurs at mid-rapidity, which is anomalous relative to $p+p$ and $p$+nucleus reactions and compared to many other heavy-ion reactions. Calculations based on cascade and thermal models fail to fit the data.