Prospects of searches for $b\to s\nu\bar{\nu}$ decays at FCC-ee

We investigate the physics reach and potential for the study of various decays involving a \bsnunu transition at the Future Circular Collider running electron-positron collisions at the $Z$-pole (FCC-ee).

Signal and background candidates, which involve inclusive $Z$ contributions from $b\bar{b}$, $c\bar{c}$ and $uds$ final states, are simulated for a proposed multi-purpose detector. Signal candidates are selected using two Boosted Decision Tree algorithms.

We determine expected relative sensitivities of $0.53\%$, $1.20\%$, $3.37\%$ and $9.86\%$ for the branching fractions of the \BdKstNuNu, \BsPhiNuNu, \BdKSNuNu and \LbLzNuNu decays, respectively.  

In addition, we investigate the impact of detector design choices related to particle-identification and vertex resolution.

The phenomenological impact of such measurements on the extraction of Standard Model and new physics parameters is also studied.