Test of lepton universality with $\hat{I}{›}_b^0\to p{K}^{-}{\ell }^{+}{\ell }^{-}$ decays

Abstract

The ratio of branching fractions of the decays $\hat{I}{›}_b^0\to p{K}^{-}{e}^{+}{e}^{-}$ and $\hat{I}{›}_b^0\to p{K}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$, $R_{pK}^{-1}$, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 $f{b}^{-1}$ recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range $0.1<q^2<6.0$ $Ge{V}^2/c^4$ and the $p{K}^{-}$ mass range $m(p{K}^{-})<2600$ $MeV/c^2$, the ratio of branching fractions is measured to be $R_{pK}^{-1}=1.17_{-0.16}^{+0.18}\pm 0.07$, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay $\hat{I}{›}_b^0\to p{K}^{-}{e}^{+}{e}^{-}$.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-040.html (LHCb public pages)