Photon Energy Spectrum in B -+ X, + y and comparison with Data

A comparison of the inclusive photon energy spectrum in the radiative decay B + X, + y, 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 m4, 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 + X, + 7) = (2.55 f 1.28) x 10m4 in the standard model, assuming ~~,~/~Vc~~ = 1.0. C om p aring this with the CLEO measurement BR(B --+ X, + +y) = (2.32 f 0.67). x 10d4 implies j&I/IVc.l = 1.1 f 0.43, in agreement with the CKM unitarity. ‘Supported by Schweizerischer Nationalfonds.