Update of the Standard Model prediction for $\bar B \to X_s \gamma$

Abstract

We report on two recent calculations on the inclusive radiative decay $\bar B\to X_s \gamma$, notably multi-parton contributions at NLO and the $Q_{1,2}-Q_7$ interference at NNLO for the physical value of the charm-quark mass. The former calculation formally completes $\bar{B} \rightarrow X_s \gamma$ at NLO in QCD at leading power, the latter removes a long-standing $\pm 3\%$ uncertainty arising from interpolation in $m_c$. The updated Standard-Model prediction for the CP- and isospin-averaged branching ratio reads ${\mathcal B}_{s \gamma}^{\rm SM} = (3.54 \pm 0.14)\times 10^{-4}$ for photon energies $E_\gamma>1.6\,{\rm GeV}$ in the $B$-meson rest frame. This value is in good agreement with the current experimental average ${\mathcal B}_{s \gamma}^{\rm exp} = (3.49 \pm 0.19)\times 10^{-4}$.