Searching for New Physics with \(\bar {\mathcal {B}}(B_{s,d}\to \mu \bar \mu )/\Delta M_{s,d}\)

Abstract

We reemphasize that the ratio $R_{s\mu} \equiv \overline{\mathcal{B}}(B_s\to\mu\bar\mu)/\Delta M_s$ is a measure of the tension of the Standard Model (SM) with latest measurements of $\overline{\mathcal{B}}(B_s\to\mu\bar\mu)$ that does not suffer from the persistent puzzle on the $|V_{cb}|$ determinations from inclusive versus exclusive $b\to c\ell\bar\nu$ decays and which affects the value of the CKM element $|V_{ts}|$ that is crucial for the SM predictions of both $\overline{\mathcal{B}}(B_s\to\mu\bar\mu)$ and $\Delta M_s$, but cancels out in the ratio $R_{s\mu}$. In our analysis we include higher order electroweak and QED corrections und adapt the latest hadronic input to find a tension of about $2\sigma$ for $R_{s\mu}$ measurements with the SM independently of $|V_{ts}|$. We also discuss the ratio $R_{d\mu}$ which could turn out, in particular in correlation with $R_{s\mu}$, to be useful for the search for New Physics, when the data on both ratios improves. Also $R_{d\mu}$ is independent of $|V_{cb}|$ or more precisely $|V_{td}|$.