# Measurements of isospin asymmetry and difference of direct $CP$ asymmetries in inclusive $B\to {X}_{s}\gamma$ decays

20 February 2019

Abstract: We report measurements of isospin asymmetry ${\Delta }_{0-}$ and difference of direct $CP$ asymmetries $\Delta {A}_{CP}$ between charged and neutral $B\to {X}_{s}\gamma$ decays. This analysis is based on the data sample containing $772×{10}^{6}B\overline{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric ${e}^{+}{e}^{-}$ collider. Using a sum-of-exclusive technique with invariant ${X}_{s}$ mass up to $2.8\text{}\text{}\mathrm{GeV}/{c}^{2}$, we obtain ${\Delta }_{0-}=\left[-0.48±1.49\left(\mathrm{stat}\right)±0.97\left(\mathrm{syst}\right)±1.15\left({f}_{+-}/{f}_{00}\right)\right]%$ and $\Delta {A}_{CP}=\left[+3.69±2.65\left(\mathrm{stat}\right)±0.76\left(\mathrm{syst}\right)\right]%$, where the last uncertainty for ${\Delta }_{0-}$ is due to the uncertainty on the production ratio of ${B}^{+}{B}^{-}$ to ${B}^{0}{\overline{B}}^{0}$ in $\Upsilon \left(4S\right)$ decays. The measured value of ${\Delta }_{0-}$ is consistent with zero, allowing us to constrain the resolved photon contribution in the $B\to {X}_{s}\gamma$, and improve the branching fraction prediction. The result for $\Delta {A}_{CP}$ is consistent with the prediction of the SM. We also measure the direct $CP$ asymmetries for charged and neutral $B\to {X}_{s}\gamma$ decays. All the measurements are the most precise to date.

Published in: Physical Review D 99 (2019)