The first measurement of the cross section ratio σttbb/σttjjis presented using a data sample corresponding to an integrated luminosity of 19.6fb−1collected in pp collisions at √s=8TeVwith the CMS detector at the LHC. Events with two leptons (eor 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 pTof both 20 and 40GeV/c. The measured ratio is 0.022 ±0.003 (stat) ±0.005 (syst)for pT\u3e20GeV/c. The absolute cross sections σttbband σttjjare also measured. The measured ratio for pT\u3e40GeV/cis compatible with a theoretical quantum chromodynamics calculation at next-to-leading order
