QCD factorization of the four-lepton decay B- -> l(v)over-bar(l)l(('))(l)over-bar(('))

Motivated by the first search for the rare chargedcurrent B decay to four leptons, l (v) over bar (l)l(('))(l) over bar ((')) , we calculate the decay amplitude with factorization methods. We obtain the B -> y* form factors, which depend on the invariant masses of the two lepton pairs, at leading power in an expansion in Lambda(QCD)/ m(b) to next-to-leading order in as, and at O(alpha(s)) at next-to-leading power. Our calculations predict branching fractions of a few times 10(-8) in the l (v) over bar (l)l(('))(l) over bar ((')) mass-squared bin up to q2 = 1 GeV2 with n+ q > 3 GeV. The branching fraction rapidly drops with increasing q2. An important further motivation for this investigation has been to explore the sensitivity of the decay rate to the inverse moment.B of the leading-twist B meson light-cone distribution amplitude. We find that in the small-q2 bin, the sensitivity to.B is almost comparable to B- -> l(-)(v) over bar (l)y when lambda.B is small, but with an added uncertainty from the light-meson intermediate resonance contribution. The sensitivity degrades with larger q(2).