Measurement of the ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }(1520){\mu }^{+}{\mu }^{-}$ differential branching fraction

The branching fraction of the rare decay ${\mathrm{\Lambda }}_b^0\to \mathrm{\Lambda }(1520){\mu }^{+}{\mu }^{-}$ is measured for the first time, in the squared dimuon mass intervals, $q^2$, excluding the $J\mathrm{/}\psi$ and $\psi (2S)$ regions. The data sample analyzed was collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of $9{\mathrm{f}\mathrm{b}}^{-1}$. The result in the highest $q^2$ interval, $q^2>15.0{\mathrm{G}\mathrm{e}\mathrm{V}}^2\mathrm{/}{c}^4$, where theoretical predictions have the smallest model dependence, agrees with the predictions.