Observation of the $ {\mathrm{J}/\psi} \to\mu^{+}\mu^{-}\mu^{+}\mu^{-} $ decay in proton-proton collisions at $ \sqrt{s} = $ 13 TeV

The $ {\mathrm{J}/\psi} \to\mu^{+}\mu^{-}\mu^{+}\mu^{-} $ decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb$ ^{-1} $. Normalizing to the $ {\mathrm{J}/\psi} \to\mu^{+}\mu^{-} $ decay mode leads to a branching fraction of $ [ $ 10.1 $ ^{+3.3}_{-2.7} $ (stat) $\pm$ 0.4 (syst) $] \times$ 10$^{-7}$, a value that is consistent with the standard model prediction. ; The J / ψ → μ + μ - μ + μ - decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6     fb - 1 . Normalizing to the J / ψ → μ + μ - decay mode leads to a branching fraction of [ 10.1 - 2.7 + 3.3 ( stat ) ± 0.4 ( syst ) ] × 10 - 7 , a value that is consistent with the standard model prediction. ; The J/$\psi$$\to$$\mu^+\mu^-\mu^+\mu^-$ decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb$^{-1}$. Normalizing to the J/$\psi$$\to$$\mu^+\mu^-$ decay mode leads to a branching fraction [10.1 $^{+3.3}_{-2.7}$ (stat) $\pm$ 0.4 (syst)] $\times$ 10$^{-7}$, a value that is consistent with the standard model prediction.