Description
The discrepancies between $b\to s\ell^+\ell^-$ data and the corresponding Standard Model predictions constitute a very intriguing hint for new physics and many scenarios that can account for these anomalies have been proposed in the literature. However, only a single light new physics explanation, with a mass below the B meson scale, is possible: a light $Z^{\prime}$ boson.
I will discuss this solution together with the impact on $B\to K^{(*)}+$invisible, Drell-Yan searches for muon pairs at LHC and $e^+e^- \to \mu^+\mu^- +$ invisible. I will point out that the forthcoming improved limits on these processes, including the experimental sensitivities required for a proper treatment of the necessarily sizeable $Z^{\prime}$ width, can rule out a $Z^{\prime}$ explanation of $b\to s\ell^+\ell^-$ data with a mass below ~4 GeV.
