Addendum: Test of lepton universality in beauty-quark decays

Addendum to: Nature Physics https://doi.org/10.1038/s41567-021-01478-8. Published online 15 March 2022.

In a new analysis since the publication of the original article, the LHCb collaboration performs a simultaneous test of muon-electron universality using ${B}^{+}\to {K}^{+}{{\mathscr{l}}}^{-}{{\mathscr{l}}}^{+}$ and ${B}^{0}\to {K}^{* 0}{{\mathscr{l}}}^{-}{{\mathscr{l}}}^{+}$ (${\mathscr{l}}=e,\mu$) decays with data collected between 2011 and 2018, corresponding to an integrated luminosity of 9 fb⁻¹(ref. ¹). Further details are provided in ref. ². The decay-rate ratios of muon to electron modes, ${R}_{K}$ and ${R}_{{K}^{* }}$, are measured in two ${q}^{2}$ regions, $0.1 < {q}^{2} < 1.1\,{\rm{G}}e{V}^{2}/{c}^{4}$ (low-${q}^{2}$) and $1.1 < {q}^{2} < 6.0\,{\rm{G}}e{V}^{2}/{c}^{4}$ (central-${q}^{2}$).

In ref. ¹ the value of ${R}_{K}$ in the central-${q}^{2}$ range is measured with the same data sample as in the initial Nature Physics publication, but different selection requirements and analysis procedures are used. The value obtained in ref. ¹, ${R}_{K}({\mathrm{central}}-{q}^{2})=0.949_{-0.041}^{+0.042}({stat})_{-0.022}^{+0.022}({syst})$, differs from the originally published result in Nature Physics. The new analysis finds that a component of the shift can be attributed to statistical effects (with a Gaussian distribution width of 0.033, as evaluated through pseudoexperiments). The main differences come from the reduction of misidentified hadronic backgrounds to the electron-decay mode due to a tighter electron particle identification working point (shift of 0.064) and the modelling of the remaining residual contribution (shift of 0.038). The new ${R}_{K}$ central-${q}^{2}$ value is compatible with the Standard Model prediction¹ and supersedes the result originally published. The numerical results initially presented in this paper should not be used as input for any meta analysis.