Measurement of B→Xγ Decays and Determination of |Vtd/Vts|

Using a sample of 383×106 BB̅ events collected by the BABAR experiment, we measure sums of seven exclusive final states B→Xd(s)γ, where Xd(Xs) is a nonstrange (strange) charmless hadronic system in the mass range 0.6–1.8  GeV/c2. After correcting for unmeasured decay modes in this mass range, we obtain a branching fraction for b→dγ of (7.2±2.7(stat)±2.3(syst))×10-6. Taking the ratio of Xd to Xs we find Γ(b→dγ)/Γ(b→sγ)=0.033±0.013(stat)±0.009(syst), from which we determine |Vtd/Vts|=0.177±0.043.