First Measurement of the cross section ratio ttbb/ttjj in pp Collisions at sqrt{s

We present the first measurement of the cross section ratio $\sigma$($t\bar{t}b\bar{b}$)/$\sigma$($t\bar{t}jj$) in the dilepton decay mode, using a data sample corresponding to an integrated luminosity of $5~\rm{fb}^{-1}$ collected in pp collisions at $\sqrt{s}$ = 7 TeV with the CMS detector at the LHC. The cross section ratio $\sigma$($t\bar{t}b\bar{b}$)/$\sigma$($t\bar{t}jj$) is measured in the visible phase space corresponding to the detector acceptance, and corrected to particle level. The measurement is performed by means of a fit to the measured multiplicity distribution of $b$-tagged jets in a sample of dileptonic top quark pair candidate events with at least four reconstructed jets. The result of the measurement, $3.6 \pm 1.1 ({\rm stat.}) \pm 0.9 ({\rm syst.}) \%$, is compared with various theory predictions.