Measurement of the $\mathrm{t}\overline{\mathrm{t}}\mathrm{b}\overline{\mathrm{b}}$ production cross section in the all-jet final state in $\mathrm{pp}$ collisions at $\sqrt{s}=13~\mathrm{TeV}$

A measurement of the production cross section of top quark pairs in association with two b jets ($\mathrm{t}\overline{\mathrm{t}}\mathrm{b}\overline{\mathrm{b}}$) is presented, using data collected in $\mathrm{pp}$ collisions at $\sqrt{s}=13~\mathrm{TeV}$ by the CMS experiment at the LHC corresponding to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. The cross section is measured in the all-jet decay channel of the top quark pairs by selecting events containing at least eight jets, of which two are identified as originating from the hadronisation of b quarks. A combination of multivariate analysis techniques is used to reduce the large background consisting uniquely of jets produced through the strong interaction, and to discriminate the jets originating from the top quark decays and additional jets. The cross section is measured for the visible $\mathrm{t}\overline{\mathrm{t}}\mathrm{b}\overline{\mathrm{b}}$ phase space, as well as for the full phase space, for which it is determined to be $5.5 \pm 0.3\text{ (stat) } ^{+1.6}_{-1.3}\text{ (syst)}~\text{pb}$. The measured cross sections are compared with predictions of several event generators and are found to be generally higher than the theoretical predictions.