Measurement of the cross section ratio sigma(t t-bar b b-bar) / sigma(t t-bar j j) in pp collisions at sqrt(s) = 8 TeV

The first measurement of the cross section ratio View the MathML sourceσtt¯bb¯/σtt¯jj is presented using a data sample corresponding to an integrated luminosity of 19.6 fb−1 collected in pp collisions at View the MathML sources=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 pTpT of both 20 and 40 GeV/c . The measured ratio is View the MathML source0.022±0.003(stat)±0.005(syst) for pT>20 GeV/cpT>20 GeV/c. The absolute cross sections View the MathML sourceσtt¯bb¯ and View the MathML sourceσtt¯jj are also measured. The measured ratio for pT>40 GeV/cpT>40 GeV/c is compatible with a theoretical quantum chromodynamics calculation at next-to-leading order.