Evidence for the simultaneous production of four top quarks in proton-proton collisions at sqrt{s} = 13 TeV

The production of four top quarks ($\mathrm{t\bar{t}t\bar{t}}$) is studied in up to $138~\mathrm{fb}^{-1}$ of LHC proton-proton collision data at a center-of-mass energy of $13~\mathrm{TeV}$. Events that have zero, one, or two opposite-sign charged electrons or muons are considered. This is the first $\mathrm{t\bar{t}t\bar{t}}$ result that includes the all-hadronic final state. The observed significance of the $\mathrm{t\bar{t}t\bar{t}}$ signal in these final states is 3.7 standard deviations (1.5 expected). The measured cross section is $38^{+13}_{-11}~\mathrm{fb}$. Combining this result with published CMS results in other final states, we obtain a significance of 3.9 standard deviations (3.2 expected), which corresponds to an observed cross section of $17^{+5}_{-5}~\mathrm{fb}$.