Soft-collinear factorization and the calculation of the B→Xsγ rate

Using results on soft-collinear factorization for inclusive B-meson decay distributions, a systematic study of the partial B -> X-s gamma decay rate with a cut E-gamma >= E-0 on photon energy is performed. For values E-0 <= 1.9 GeV the rate can be calculated without reference to shape functions. The result depends on three large scales: M-b, root m(b)Delta, and Delta = m(b) - 2E(0). The sensitivity to the scale Delta approximate to 1.1 GeV (for E-0 approximate to 1.8 GeV) introduces significant uncertainties, which have been ignored in the past. Our new prediction for the B -> X-s gamma branching ratio with E gamma >= 1.8 GeV is Br(B -> X-s gamma) = (3.44 +/- 0.53 +/- 0.35) X 10(-4), where the errors refer to perturbative and parameter uncertainties, respectively. The implications of larger theory uncertainties for New Physics searches are explored with the example of the type-II two-Higgs-doublet model.