$B_s\to K^{(*)0}{\overline{K}}^{(*)0}$ $CP$ Asymmetries: Golden Channels for New Physics Searches

We point out that time-dependent $CP$ asymmetries in $B_s\to K^{*0}{\overline{K}}^{*0}$ decays probe the presence of new physics in $b\to s$ transitions with an unprecedented theoretical accuracy. We show that, contrary to the case of $B_d\to \varphi K_S$, it is possible to obtain a model-independent prediction for the coefficient $S(B_s\to K^{*0}{\overline{K}}^{*0})$ in the standard model. We give an estimate of the experimental precision achievable with the next generation of $B$ physics experiments. We also discuss how this approach can be extended to the case of $B_s\to {\overline{K}}^{*0}{K}^0$, $B_s\to K^{*0}{\overline{K}}^0$, and $B_s\to K^0{\overline{K}}^0$ decays and the different experimental challenges for these channels.