W/Z + jets in ATLAS

W/Z+jets events allow to study the performance of the detector, calibrate jet energy scale, and validate measurement tools and methods. Once sufficient precision is obtained on W/Z+jets measurements, constraints on PDF and QCD higher ordre perturbative corrections can be obtained. The first W/Z+jets analyses performance within ATLAS with 1pb-1 of data already allow to probe NLO QCD effects, while setting the ground for precise measurement of these processes. After a review of the data to MC comparison made with W/Z+jets events, a survey of the major source of systematic uncertainties and how they are handle in ATLAS is presented. With the high precision expected with 2011 measurements, small effects that we neglected in the past will become significant. This presentation want to already start the discussion inside the wider HEP community on the best approaches to these effects. Point to be discussed in the workshop are the treatement of QED FSR corrections, choice of jet energy threshold, problem of electron-jet overlap and comparison of parton-level to particle level predictions.