  Direct CP violation can occur in B-meson decays of the type b -> d+c+cbar,
where the charm-anticharm pair forms a J/psi. The CP asymmetry requires the
contribution to the amplitude from decays into other states, which rescatter
into d+J/psi via final state interactions. In particular, states with the same
quark content as d+J/psi can contribute. A perturbative calculation, based on a
quark level description of the rescattering process, gives an asymmetry of
about 1%, due to this effect. This makes it the dominant contribution to the
asymmetry, as suggested by an earlier estimate, based on an hadronic picture.
