Test of lepton flavour universality with $B^{+}\to K^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}{\ell }^{+}{\ell }^{-}$ decays

Abstract

The first test of lepton flavor universality between muons and electrons using $B^{+}\to K^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}{\ell }^{+}{\ell }^{-}$ ($\ell =e,\hat{I}¼$) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. The ratio of branching fractions between $B^{+}\to K^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}{e}^{-}$ and $B^{+}\to K^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$decays is measured in the dilepton invariant-mass-squared range $1.1<q^2<7.0{\mathrm{GeV}}^2/c^4$ and is found to be $R_{K\ddot{I}€\ddot{I}€}^{-1}=1.31_{-0.17}^{+0.18}(\mathrm{stat}){}_{-0.09}^{+0.12}(\mathrm{syst})$, in agreement with the standard model prediction. The first observation of the $B^{+}\to K^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}{e}^{-}$ decay is also reported.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1606/ (LHCb public pages)