Measurements of the B -> X-s gamma branching fraction and photon spectrum from a sum of exclusive final states

Using 88.9 million BB̅ events collected by the BABAR detector at the Υ(4S), we measure the branching fraction for the radiative penguin process B→Xsγ from the sum of 38 exclusive final states. The inclusive branching fraction above a minimum photon energy Eγ>1.9  GeV is B(b→sγ)=(3.27±0.18(stat)-0.40+0.55(syst)-0.09+0.04(theory))×10-4. We also measure the isospin asymmetry between B-→Xsu̅ γ and B̅ 0→Xsd̅ γ to be Δ0-=-0.006±0.058(stat)±0.009(syst)±0.024(B̅ 0/B-). The photon energy spectrum is measured in the B rest frame, from which moments are derived for different values of the minimum photon energy. We present fits to the photon spectrum and moments which give the heavy-quark parameters mb and μπ2. The fitted parameters are consistent with those obtained from semileptonic B→Xcℓν decays, and are useful inputs for the extraction of |Vub| from measurements of semileptonic B→Xuℓν decays.