Complete NNLO QCD analysis of (B)over-bar→Xsl+l- and higher order electroweak effects -: art. no. 071

We complete the next-to-next-to-leading order QCD calculation of the branching ratio for (B) over bar --> X(s)l(+) l(-) including recent results for the three-loop anomalous dimension matrix and two-loop matrix elements. These new contributions modify the branching ratio in the low-q(2) region, BRll, by about +1% and -4%, respectively. We furthermore discuss the appropriate normalization of the electromagnetic coupling alpha and calculate the dominant higher order electroweak effects, showing that, due to accidental cancellations, they change BRll by only -1.5% if alpha(mu) is normalized at mu = O(m(b)), while they shift it by about -8.5% if one uses a high scale normalization mu = O(M-w). The position of the zero of the forward-backward asymmetry, q(0)(2) is changed by around +2%. After introducing a few additional improvements in order to reduce the theoretical error, we perform a comprehensive study of the uncertainty. We obtain BRll (1 GeV2 less than or equal to q(2) less than or equal to 6 GeV2) = (1.57 +/- 0.16) x 10(-6) and q(0)(2) = (3.76 +/- 0.33) GeV2 and note that the part of the uncertainty due to the b-quark mass can be easily reduced.