Quasifree subthreshold pion production in the reaction C12(p,dπ+)11B

Nuclear pion production has been studied by means of the reaction C-12(p,d-pi+)B-11 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 --> pi+ + d.