Quasifree subthreshold pion production in the reactionC12(p,dπ+)11B

Nuclear pion production has been studied by means of the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,d${\mathrm{\pi }}^{+}$ ${)}^{11}$B at an incident energy of 223 MeV, which is considerably below the threshold for a free N-N process. The shape and absolute cross section of the experimental energy-sharing distribution are in remarkable agreement with the prediction of a distorted-wave impulse approximation theory. This shows that the reaction mechanism is quasifree pion production, which is related to the elementary reaction p+p→${\mathrm{\pi }}^{+}$+d.