Measurements of the B→Xsγ branching fraction and photon spectrum from a sum of exclusive final states

Using 88.9 million BB̄ 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>1.9GeV 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- →Xsūγ and B̄0→Xsd̄γ to be Δ0-=-0.006±0.058(stat)±0.009(syst)±0.024(B̄0/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→Xc ν decays, and are useful inputs for the extraction of |Vub| from measurements of semileptonic B→Xu ν decays.