Distortion effects in a relativistic one-nucleon model for the (p,π+) reaction

A relativistic distorted-wave Born approximation model is developed for (p,π+) reactions within the framework of the one-nucleon mechanism. The nucleon motion is described by solutions to the Dirac equation with appropriate nuclear potentials. Distortion effects in both the proton and pion channels are taken into account and are found to be important. Both pseudovector and pseudoscalar forms of the πNN vertex are considered. The former is found to lead invariably to better agreement with the data. Calculations have been carried out for proton energies < or =200 MeV. Good agreement is obtained with the cross section data for reactions on 40Ca and 16O leading to the ground state of the residual nucleus. For reactions on 12C, the cross section shapes, but not their magnitudes, are reproduced. The calculated analyzing powers are found to be in good agreement with the forward angle data