Measurement of the jet multiplicity in top anti-top final states produced in 7 TeV proton-proton collisions with the ATLAS detector

The reconstructed jet multiplicity is presented for an enhanced top anti-top event selection, at a centre-of-mass energy of 7 TeV, and for the transverse momentum thresholds of 25, 40, 60 and 80 GeV. The ttbar enhanced region is defined by lepton transverse momentum, missing transverse energy, transverse W mass, b-tagging and jet multiplicity requirements. Results are shown for an integrated luminosity of 4656pb-1 +- 1.8%. The reconstructed spectra are corrected for detector effects within a kinematic range closely matched to the experimental acceptance. The measurements are compared to several Monte Carlo models, which include fixed order matrix element calculations and experimentally motivated ISR/FSR variations.