Electroproduction of charged pions from light nuclei

Abstract

Electroproduction of charged pi mesons from light nuclei to discrete final states is studied in a distorted wave impulse approximation. The Blomqvist and Laget pion photoproduction operator is extended to the case of electroproduction by including virtual photons. Gauge invariance is included in the theory by making the Feynman diagrams for the process individually gauge invariant. Conservation of the electroproduction current and isolation of the electron's kinematical aspects are done by introducing modified virtual photon polarization vectors. Cross section calculations for single nucleon electroproduction performed with the real photoproduction parameters of Blomqvist and Laget and standard forms of electromagnetic form factors agree with data. The single nucleon virtual photoproduction operator is used in a distorted wave impulse approximation to describe electroproduction from a nuclear target leading to a discrete final nuclear state. Nuclear transition densities which enter into elastic electron scattering and electroproduction processes are compared. It is found that because of the change of nuclear isospin, electroproduction provides information on a larger number of transition densities than inelastic electron scattering for a given target nucleus. Methods of integrating over the electron's kinematics are presented for single arm experiments, that is, where only the produced pion is detected. Single arm electroproduction cross sections are calculated for 10B and 12C targets. For the 10B case, good agreement with data is found. For the 12C electroproduction cross sections, no conclusions can be reached because the quality of present data is poor. It is found that in these experiments, contributions to the cross section from longitudinal virtual photon components are negligible because of small values of virtual photon invariant mass.