Measurement of ttbb production rate in final state with lepton+jets and the cross section ratio ttbb/ttjj at 8 TeV with the CMS detector

The cross sections of the associated production of a top-quark pair with at least two additional jets or two additional b jets are measured in the final state with one lepton and jets. The study is performed for an integrated luminosity of 19.6 fb$^{-1}$ at a center-of-mass energy of $\sqrt{s}$\,=\,8 TeV. To identify the jets originating from the top-quark pair decay a kinematic fit with mass constraints, multivariate classifiers in categories split by the jet multiplicity and b-tag discriminants of the jets are used. The contributions of $\rm{t\bar{t}b\bar{b}}$ and $\rm{t\bar{t}jj}$ with at least two additional b jets or jets of any flavor are measured with a simultaneous template fit using shapes of b-tag discriminants. The measured cross sections $\sigma(\rm{t\bar{t}b\bar{b}}) =271.0 \pm 103.0(stat)\pm 32.2(syst)\pm 7.0(lumi)$ fb, $\sigma(\rm{t\bar{t}jj}) = 23.1 \pm 2.3(stat)\pm 2.9(syst)\pm 0.6(lumi)$ pb and the cross section ratio $\sigma(\rm{t\bar{t}b\bar{b}})$/$\sigma(\rm{t\bar{t}jj}) = 0.0117 \pm 0.0040(\rm{stat}) \pm 0.0003(\rm{syst})$ correspond to the phase space of additional jets defined at generator-level as: $p_{\rm{T{aj}}}> 40\,$GeV/c, $\left\vert \eta_{\rm aj}\right\vert<$2.5, $\Delta \rm R_{\rm ajj} >$ 0.5. The parton with leading transverse momentum inside the cone of the jet defines the jet flavor. The obtained results agree with the NLO calculations and with the measurement of CMS in the dilepton channel when the same jet definition is used.