Reduction of Charm Quark Mass Scheme Dependence in $\bar{B}\to X_s\gamma$ at the NNLL Level

The uncertainty of the theoretical prediction of the $\bar{B}\to X_s\gamma$ branching ratio at NLL level is dominated by the charm mass renormalization scheme ambiguity. In this paper we calculate those NNLL terms which are related to the renormalization of $m_c$, in order to get an estimate of the corresponding uncertainty at the NNLL level. We find that these terms significantly reduce (by typically a factor of two) the error on ${BR}(\bar B \to X_s \gamma)$inducedbythedefinitionof$m_c$. Taking into account the experimental accuracy of around 10% and the future prospects of the $B$ factories, we conclude that a NNLL calculation would increase the sensitivity of the observable $\bar{B}\to X_s\gamma$ to possible new degrees of freedom beyond the SM significantly.