  Effects of the superconducting pair potential on the impurity scattering
processes in metallic carbon nanotubes are studied theoretically. The backward
scattering of electrons vanishes in the normal state. In the presence of the
superconducting pair correlations, the backward scatterings of electron- and
hole-like quasiparticles vanish, too. The impurity gives rise to backward
scatterings of holes for incident electrons, and it also induces backward
scatterings of electrons for incident holes. Negative and positive currents
induced by such the scatterings between electrons and holes cancel each other.
Therefore, the nonmagnetic impurity does not hinder the supercurrent in the
regions where the superconducting proximity effects occur, and the carbon
nanotube is a good conductor for Cooper pairs. Relations with experiments are
discussed.
