  The normalised differential top quark-antiquark production cross section is
measured as a function of the jet multiplicity in proton-proton collisions at a
centre-of-mass energy of 7 TeV at the LHC with the CMS detector. The
measurement is performed in both the dilepton and lepton + jets decay channels
using data corresponding to an integrated luminosity of 5.0 inverse femtobarns.
Using a procedure to associate jets to decay products of the top quarks, the
differential cross section of the t t-bar production is determined as a
function of the additional jet multiplicity in the lepton + jets channel.
Furthermore, the fraction of events with no additional jets is measured in the
dilepton channel, as a function of the threshold on the jet transverse
momentum. The measurements are compared with predictions from perturbative
quantum chromodynamics and no significant deviations are observed.
