The photon energy spectrum in B→Xs+γ in perturbative QCD through O(αs2)

We derive the dominant part of the O(αs2) correction to the photon energy spectrum in the inclusive decay B→Xs+γ. The detailed knowledge of the spectrum is important for relating the theoretical calculations of the B→Xs+γ decay rate and the experimental measurements where a cut on the photon energy is applied. In addition, moments of the photon energy spectrum are used for the determination of the b-quark mass and other fundamental parameters of heavy quark physics. Our calculation reduces the theoretical uncertainty associated with uncalculated higher orders effects and shows that, for B→Xs+γ, QCD radiative corrections to the photon energy spectrum are under theoretical control.