The first measurement of the cross section ratio σttbb/σttjj is presented using a data sample corresponding
to an integrated luminosity of 19.6 fb−1 collected in pp collisions at √s = 8 TeV with the CMS detector at
the LHC. Events with two leptons (e or μ) and four reconstructed jets, including two identified as b quark
jets, in the final state are selected. The ratio is determined for a minimum jet transverse momentum pT
of both 20 and 40 GeV/c. The measured ratio is 0.022 ± 0.003 (stat) ± 0.005 (syst) for pT > 20 GeV/c.
The absolute cross sections σttbb and σttjj are also measured. The measured ratio for pT > 40 GeV/c is
compatible with a theoretical quantum chromodynamics calculation at next-to-leading order.