  The normalised differential top quark-antiquark production cross section is
measured as a function of the jet multiplicity. Using a procedure to associate
jets to decay products of the top quarks, the differential cross section of the
ttbar production is determined as a function of the additional jet
multiplicity. The fraction of events with no additional jets is measured as a
function of the threshold required for the transverse momentum of the
additional jet. The measurements are compared with predictions from
perturbative quantum chromodynamics and no significant deviations are observed.
