Evidence for the decay $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}

A search for the decay $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ B S 0 → K ¯ ∗ 0 μ + μ − is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb −1 of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ B S 0 → K ¯ ∗ 0 μ + μ − decay is determined to be $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}\right)=\left[2.9\pm 1.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\pm 0.3\left(\mathrm{norm}\right)\right]\times {10}^{-8} $$ ℬ B s 0 → K ¯ ∗ 0 μ + μ − = 2.9 ± 1.0 stat ± 0.2 syst ± 0.3 norm × 10 − 8 , where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.