Measurement of Jet Multiplicity Distributions in Top Quark Pair Events with Two Leptons in the Final State at a center of mass energy of 7 TeV.

The jet activity in top-antitop quark pair events is measured in pp collisions at a center of mass energy of 7 TeV with the CMS detector using a dataset recorded in 2011 corresponding to an integrated luminosity of 5.0/fb. The measurement is performed in the dileptonic decay channels (where the two W bosons decay to leptons) of the top-antitop quark pairs, with at least two isolated leptons and at least one b-jet in the final state. The differential top anti-top quark cross section is measured as a function of the jet multiplicity. Furthermore, the distribution of the fraction of events without additional jets above a momentum threshold is measured. Several QCD calculations are compared with the data.