Measurement of the cross section for $\text{t}\bar{\text{t}}$ production with additional jets and b jets in pp collisions at $\sqrt{s} =$ 13 TeV
Measurements of the cross section for the production of top quark pairs in association with a pair of jets from bottom quarks ($\sigma_\mathrm{t\bar{t}b\bar{b}}$) and in association with a pair of jets from quarks of any flavor or gluons ($\sigma_\mathrm{t\bar{t}jj}$) and their ratio are presented. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The measurements are performed in a fiducial phase space and extrapolated to the full phase space, separately in the dilepton and lepton+jets channels, where lepton corresponds to either an electron or a muon. The results for the dilepton and lepton+jets channels, respectively, are $\sigma_\mathrm{t\bar{t}jj}$ = 2.36 $\pm$ 0.02 (stat) $\pm$ 0.20 (syst) pb and 31.0 $\pm$ 0.2 (stat) $\pm$ 2.9 (syst) pb, and for the cross section ratio 0.017 $\pm$ 0.001 (stat) $\pm$ 0.001 (syst) and 0.020 $\pm$ 0.001 (stat) $\pm$ 0.001 (syst). The values of $\sigma_\mathrm{t\bar{t}b\bar{b}}$ are determined from the product of the $\sigma_\mathrm{t\bar{t}jj}$ and the cross section ratio, obtaining, respectively, 0.040 $\pm$ 0.002 (stat) $\pm$ 0.005 (syst) pb and 0.62 $\pm$ 0.03 (stat) $\pm$ 0.07 (syst) pb. These measurements are the most precise to date and are consistent, within the uncertainties, with the standard model expectations obtained using a matrix element calculation at next-to-leading order in quantum chromodynamics matched to a parton shower.