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

Bondu, Olivier [UCL] Bruno, Giacomo [UCL] Caputo, Claudio [UCL] David, Pieter [UCL] Delaere, Christophe [UCL] Delcourt, Martin [UCL] Giammanco, Andrea [UCL] Lemaitre, Vincent [UCL] Prisciandaro, Jessica [UCL] Saggio, Alessia [UCL] Vidal Marono, Miguel [UCL] Vischia, Pietro [UCL] Zobec, Joze [UCL] CMS Collaboration et al.

The observation of the $\Lambda_\mathrm{b}^0 \to$J/$\psi \Lambda \phi$ decay is reported using proton-proton collision data collected at $\sqrt{s} =$ 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 $\mathcal{B}(\Lambda_\mathrm{b}^0 \to$J/$\psi \Lambda \phi)/\mathcal{B}(\Lambda_\mathrm{b}^0\to\psi \Lambda)$ is measured to be (8.26$\pm$0.90 (stat) $\pm$ 0.68 (syst) $\pm$ 0.11 $(\mathcal{B}))\times $10$^{-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 $\phi$ and $\psi$(2S) decays to the reconstructed final states.