Observation of the decay $\mathrm{Z}\to \psi {\ell }^{+}{\ell }^{-}\to {\mu }^{+}{\mu }^{-}{\ell }^{+}{\ell }^{-}$ with the CMS detector

S. Leontsinis

The observation of the $\mathrm{Z}$ boson rare decay to a $\psi$ meson and two oppositely charged same-flavour leptons, ${\ell }^{+}{\ell }^{-}$, where $\psi$ represents the sum of $\mathrm{J}/\psi$…