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Test of lepton universality with \( {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} \) decays

A preprint version of the article is available at arXiv.


The ratio of branching fractions of the decays \( {\Lambda}_b^0 \)pKe+e and \( {\Lambda}_b^0 \)pKμ+μ, \( {R}_{pK}^{-1} \), is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q2 < 6.0 GeV2/c4 and the pK mass range m(pK) < 2600 MeV/c2, 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 \( {\Lambda}_b^0 \)pKe+e.


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