Photon energy spectrum in B $\to$ $X_S$ + $\gamma$ and comparison with data

A comparison of the inclusive photon energy spectrum in the radiative decay B → XS + γ, measured recently by the CLEO Collaboration, with the standard model is presented, using a B-meson wave function model and improving earlier perturbative QCD-based computations of the same. The dependence of the photon energy spectrum on the non-perturbative model parameters, pF, the b-quark Fermi momentum in the B hadron, and mq, the spectator quark mass, is explicitly shown, allowing a comparison of these parameters with the ones obtained from the analysis of the lepton energy spectrum in semileptonic B decays. Taking into account present uncertainties, we estimate BR(B → Xs + γ) = (2.55 ± 1.28) × 10−4 in the standard model, assuming . Comparing this with the CLEO measurement BR(B → Xs + γ) = (2.32±0.67) × 10−4 implies , in agreement with the CKM unitarity