,C12(p→,π±) reactions atTp=200 MeV

The results of a comparative study of the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}\to$,${\pi }^{\pm }$) and ${}_{}{}^{12}{}_{}{}^{}(\mathit{p}\to$,${\pi }^{+}$) reactions at $T_p$=200 MeV and 30°≤${\theta }_{\mathrm{lab}{}^{\pi }\mathrm{\le }150\mathrm{°}}$ are reported. The isospin-dependence of the NN→NNπ processes inside nuclei is investigated by comparing cross sections and analyzing powers for the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) continuum production to those for corresponding NN→NNπ processes in the free case. The comparison favors the dominance of a quasifree two-nucleon mechanism in nuclear pion production. Relative populations of discrete final states in the ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) spectra are compared, confirming the dominance of the two-nucleon mechanism and suggesting the identification of some high-spin states in the mirror nuclei ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{O}$. Cross-section and analyzing power angular distributions are presented for discrete final states populated strongly in ${}_{}{}^{13}{}_{}{}^{}(\mathit{p}$,${\pi }^{\pm }$) and ${}_{}{}^{12}{}_{}{}^{}(\mathit{p}$,${\pi }^{+}$) up to 24 MeV excitation energy. Cross-section data for a number of ${}_{}{}^{12}{}_{}{}^{}$,13C(p,${\pi }^{+}$) transitions are compared to (p,${\pi }^{+}$) shell-model calculations employing the elementary pp→d${\pi }^{+}$ amplitude along with realistic nuclear wave functions. Isolated anomalous features exhibited by strong ${}_{}{}^{12}{}_{}{}^{}$,13C(p,${\pi }^{+}$) transitions to two highly excited discrete states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ are discussed and alternative possible interpretations for these states are presented.