Observation of the $\Lambda_\mathrm{b}^0 \to$ J/$\psi \Lambda \phi$ decay in proton-proton collisions at $\sqrt{s}=$ 13 TeV

The observation of the 0
b → J/ψφ decay is reported using proton-proton collision data collected at
√s = 13 TeV by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity
of 60 fb−1. The ratio of the branching fractions B(0
b → J/ψφ)/B(0
b → ψ(2S)) is measured to be
(8.26 ± 0.90 (stat) ± 0.68 (syst) ± 0.11(B)) × 10−2, where the first uncertainty is statistical, the second is
systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of
φ and ψ(2S) decays to the reconstructed final states.