Search for standard model production of four top quarks with the single-lepton and opposite-sign dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search for the standard model production of four top quarks ($\mathrm{pp \rightarrow t\bar{t}t\bar{t}}$) is reported using events with single-lepton ($\mathrm{e}$, $\mu$) + jets and opposite-sign dilepton ($\mu^+\mu^-$, $\mu^\pm \mathrm{e}^\mp$, or $\mathrm{e^+e^-}$) + jets signatures. The events are collected in proton-proton collisions recorded by the CMS detector at the LHC at $\sqrt{s}=13$ TeV in a sample corresponding to an integrated luminosity of 35.8 fb$^{-1}$. A multivariate analysis using global event and jet properties based on boosted decision trees is used to discriminate $\mathrm{t\bar{t}t\bar{t}}$ from $\mathrm{t\bar{t}}$ production. No significant deviation is observed from the predicted background. An upper limit is set on the cross section for $\mathrm{t\bar{t}t\bar{t}}$ production in the standard model of 48 fb at 95$\%$ confidence level. When combined with the previous measurement of $\sigma_\mathrm{t\bar{t}t\bar{t}}$ by the CMS experiment from an analysis of other final states, the observed signal significance is 1.4 standard deviations and the combined cross section measurement is $\sigma_\mathrm{t\bar{t}t\bar{t}} = 13^{+11}_{-9}$ fb.