Chromomagnetic Dipole-Operator Corrections in Bbar -> X_sgamma at O(beta_0 alpha_s^2)

TL;DR

This paper computes higher-order fermionic corrections to the photon-energy spectrum in Bbar -> X_sgamma decay, refining theoretical predictions for the branching ratio by including next-to-next-to-leading order effects from the chromomagnetic dipole operator.

Contribution

It introduces the calculation of fermionic corrections at O(beta_0 alpha_s^2) for the Bbar -> X_sgamma decay, specifically from the self-interference of the Q_8 operator, which was not previously evaluated.

Findings

O(beta_0 alpha_s^2) correction shifts the branching ratio by +0.12% at 1.6 GeV photon cut.

Correction results in a +0.27% shift at 1.0 GeV photon cut.

Comments on the potential impact of resummation and non-perturbative effects.

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.