Exclusive rare B → K*l+l- decays at low recoil:: Controlling the long-distance effects -: art. no. 114005

We present a model-independent description of the exclusive rare decays (B) over bar -->K*e(+)e(-) in the low recoil region (large lepton invariant mass q(2)similar tom(b)(2)). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in 1/Q, with Q={m(b),rootq(2)}. Nonperturbative effects up to and including terms suppressed by Lambda/Q and m(c)(2)/m(b)(2) relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the Cabibbo-Kobayashi-Maskawa matrix element \V-ub\ from a combination of rare and semileptonic B and D decays near the zero recoil point. The residual theoretical uncertainty from long-distance effects in this \V-ub\ determination comes from terms in the operator product expansion of order alpha(s)(Q)Lambda/m(b), alpha(s)(2)(Q), m(c)(4)/m(b)(4), and duality violations, and is estimated to be below 10%.