An explicit estimate of charm rescattering in B->Kll

We analyze B0→K0ℓ¯ℓ long-distance contributions induced by the rescattering of a pair of charmed and charmed-strange mesons. We present an explicit estimate of these contributions using an effective description in terms of hadronic degrees of freedom, supplemented by data on the B0→D*Ds(Ds*D) transition in order to reproduce the corresponding discontinuity in the B0→K0ℓ¯ℓ amplitude. The D*Ds(Ds*D)K vertex is estimated using heavy-hadron chiral perturbation theory, obtaining an accurate description of the whole rescattering process in the low-recoil (or high-q2) limit. We also present an extrapolation to the whole kinematical region introducing hadronic form factors. The explicit estimate of the leading D*Ds(Ds*D) intermediate state leads to a long-distance amplitude which does not exceed a few percent relative to the short-distance one. The consequences of this result for the extraction of the short-distance coefficient C9 are discussed.