Measurement of the production cross section for W-bosons in association with jets in $pp$ collisions using 33 pb-1 at sqrt(s) = 7 TeV with the ATLAS detector

This note reports on the measurement of the inclusive $W$+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 \TeV~a t the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the $W$ boson, are presented as a function of je t multiplicity. Also presented are differential cross sections as a function of the transverse momentum of the first jet in $\ge 1\rm{-}4$ jet ev ents, the second jet in $ \ge 2\rm{-}4$ jet events, the third jet in $ \ge 3\rm{-}4$ jet events and the fourth jet in $ \ge 4$ jet events. The di fferential cross section as a function of \HT~for $\ge 1\rm{-}4$ jet events are also shown. Measurements are presented of the ratio of cross sect ions $\sigma(W+ \ge n)/\sigma(W+ \ge n-1)$ for inclusive jet multiplicities $n=1\rm{-}5$. The results, based on an integrated luminosity of 33.3 \ipb, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The mea sured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations from MCFM and BLAC KHAT-SHERPA, studied here for $n \le 3$, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.