Photon energy spectrum in B →Xs + γ 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)x10-4 in the standard model, assuming vertical stroke Vtsvertical stroke /vertical stroke Vcbvertical stroke =1.0. Comparing this with CLEO measurement BR(B→Xs+γ)=(2.32±0.67)x10-4 implies vertical stroke Vtsvertical stroke /vertical stroke Vcbvertical stroke =1.1±0.43, in agreement with the CKM unitarity. (orig.)