Exclusive Measurements of b → sγ Transition Rate and Photon Energy Spectrum

We use 429 fb⁻¹ of e⁺e⁻ collision data collected at the Υ(4S) resonance with the BABAR detector to measure the radiative transition rate of b → sγ with a sum of 38 exclusive final states. The inclusive branching fraction with a minimum photon energy of 1.9 GeV is found to be ℬ(B̅ → Χ_sγ) = (3.29 ± 0.19 ± 0.48) x 10⁻⁴ where the first uncertainty is statistical and the second is systematic. We also measure the first and second moments of the photon energy spectrum and extract the best-fit values for the heavy-quark parameters, m_b and μ_π², in the kinetic and shape function models.