Differential cross sections for the neutral pion production reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\mathrm{\pi }}^0$${)}^{13}$${\mathrm{N}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ have been measured at 153.5, 166.1, 186.0, and 204.0 MeV bombarding energy using recoil detection. The shape of the angular distribution agrees well with that of the mirror reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\mathrm{\pi }}^{+}$${)}^{13}$${\mathrm{C}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$. Isospin invariance predicts for the ratio of the cross sections σ(p,${\mathrm{\pi }}^{+}$)/σ(p,${\mathrm{\pi }}^0$)=2. At 153.5, 166.1, and 186.0, MeV, where (p,${\mathrm{\pi }}^{+}$) cross sections have been reported previously by other groups at the same reduced pion momentum η=${\mathit{p}}_{\mathrm{\pi }}$/${\mathit{m}}_{\mathrm{\pi }}$c=0.34,0.55,0.78, the ratio of the total cross sections is 2.02±0.14, 3.14±0.12, and 2.12±0.16, respectively. The (p,${\mathrm{\pi }}^0$) cross sections at 166 MeV is therefore 1.57±0.06 times larger than expected. For ${\mathit{T}}_{\mathit{p}}$<160 MeV, the experimental cross sections are larger than predicted by a phase space and Coulomb barrier penetration calculation that fits the higher-energy data. Differential cross sections were also obtained for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\mathrm{\pi }}^{\mathrm{-}}$${)}^{13}$O reaction, and upper limits set for differential cross sections for radiative capture to the ground state of ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$.

• Received 17 October 1991

DOI:https://doi.org/10.1103/PhysRevC.45.1276