Tests of lepton universality in $B^0\to K_S^0{\ell }^{+}{\ell }^{-}$ and $B^{+}\to K^{*+}{\ell }^{+}{\ell }^{-}$ decays where $\ell$ is either an electron or a muon are presented. The differential branching fractions of $B^0\to K_S^0{e}^{+}{e}^{-}$ and $B^{+}\to K^{*+}{e}^{+}{e}^{-}$ decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The results are consistent with the standard model and previous tests of lepton universality in related decay modes. The first observation of $B^0\to K_S^0{e}^{+}{e}^{-}$ and $B^{+}\to K^{*+}{e}^{+}{e}^{-}$ decays is reported.

• Received 19 October 2021
• Accepted 29 March 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.191802

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