Chromomagnetic dipole-operator corrections inB¯→XsγatO(β0αs2)

Abstract

We calculate the fermionic corrections to the photon-energy spectrum of Bbar -> X_sgamma which arise from the self-interference of the chromomagnetic dipole operator Q_8 at next-to-next-to-leading order by applying naive non-abelianization. The resulting O(beta_0 alpha_s^2) correction to the Bbar -> X_sgamma branching ratio amounts to a relative shift of +0.12% (+0.27%) for a photon-energy cut of 1.6 GeV (1.0 GeV). We also comment on the potential size of resummation and non-perturbative effects related to Q_8.