Nuclear effects in positive pion electroproduction on the deuteron near threshold

Abstract

Positive pion electroproduction from the deuteron near threshold has been considered within an approach based on the unitary transformation method. The gauge independence of the treatment is provided by using an explicitly gauge independent expression for the reaction amplitude. The results of calculations for kinematics of the experiments on forward-angle $π^+$ meson electroproduction accomplished at Saclay and Jefferson Laboratory are discussed and compared with those given by the impulse approximation. It is shown that the observed behaviour of the cross sections is in accordance with the calculations based on the pion-nucleon dynamics. In particular, the pion production rate suppression in the $^2H(e,e'π^+)nn$ reaction compared to that for the $^1H(e,e'π^+)n$ one can be due to such ``nuclear medium'' effects as nucleon motion and binding along with Pauli blocking in the final $nn$ state.