LHCb CollaborationAlfonso Albero, AlejandroCalvo Gómez, MíriamCamboni, AlessandroCoquereau, SamuelGarrido Beltrán, LluísGascón Fora, DavidGironella Gironell, PereGolobardes, E.Graciani Díaz, RicardoGraugés Pous, EugeniManera Escalero, R.Marin Benito, CarlaVázquez Gómez, RicardVilasis-Cardona, Xavier2022-05-042022-05-042020-05-111126-6708https://hdl.handle.net/2445/185367The ratio of branching fractions of the decays Λ0b → pK−e+e− and Λ0b → pK−μ+μ−, R−1pK, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb−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 < 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−1pK=1.17+0.18−0.16±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 Λ0b → pK−e+e−.27 p.application/pdfengcc-by (c) LHCb Collaboration et al., 2020https://creativecommons.org/licenses/by/4.0/HadronsGran Col·lisionador d'HadronsFísica de partículesExperimentsHadronsLarge Hadron Collider (France and Switzerland)Particle physicsExperimentsinfo:eu-repo/semantics/article7102422022-05-04info:eu-repo/semantics/openAccess