A measurement of the ratio of the production cross sections for W and Z bosons in association with jets with the ATLAS detector

The ratio of the production cross sections for $W$ and $Z$ bosons in association with jets has been measured in proton--proton collisions at $\sqrt{s}=7\,\mathrm{TeV}$ with the ATLAS experiment at the Large Hadron Collider. The measurement includes the entire 2011 data set, corresponding to an integrated luminosity of $4.6\,\mathrm{fb}^{-1}$. Inclusive and differential cross-section ratios for massive vector bosons decaying to electrons and muons are measured in association with jets with transverse momentum $p_\mathrm{T} >30\,\mathrm{GeV}$ and jet rapidity $|y| < 4.4$. The measurements are compared to next-to-leading-order perturbative QCD calculations and to predictions from different Monte Carlo generators implementing leading-order matrix elements supplemented by parton showers.