On the Standard Model predictions for $R_K$ and $R_{K^{\ast }}$

Abstract

We evaluate the impact of radiative corrections in the ratios $\Gamma [B\to M{\mu }^{+}{\mu }^{-}]/\Gamma [B\to M{e}^{+}{e}^{-}]$ when the meson $M$ is a $K$ or a $K^{\ast }$. Employing the cuts on $m_{\ell \ell }^2$ and the reconstructed $B$-meson mass presently applied by the LHCb Collaboration, such corrections do not exceed a few $\%$. Moreover, their effect is well described (and corrected for) by existing Montecarlo codes. Our analysis reinforces the interest of these observables as clean probe of physics beyond the Standard Model.

6 pages [v3: Added Note on SM predictions for RK* in the low q2 region]