Measurement of the branching fraction of the Λb0→J/ψΛ decay and isospin asymmetry of B → J/ψK decays

This paper describes a measurement of the Λb0→J/ψΛ branching fraction using data collected with the LHCb experiment in proton-proton collisions from 2016 to 2018. The dataset corresponds to an integrated luminosity of 5.4 fb⁻¹. The branching fraction is determined relative to that of B0→J/ψKS0 decays, (Formula presented.) yielding BΛb0→J/ψΛ=3.34±0.02±0.10±0.08±0.28×10−4, where the first uncertainty is statistical, the second systematic, the third due to external inputs on branching fractions and the fourth due to the ratio of Λb0 baryon and B⁰ meson hadronisation fractions. In addition, the isospin asymmetry between the rates of B0→J/ψKS0 and B⁺→ J/ψK⁺ decays is measured to be (Formula presented.) where the first uncertainty is statistical and the second systematic.