A technique for measuring the pp->Z+X background to the H4l channel for the discovery of the Higgs Boson at LHC

A method for simultaneously extracting the dominant pp to Z+X and pp to ZZ backgrounds in the H to 4l signal region from early ATLAS measurements, is proposed. The main focus is in predicting the yield of the Z boson background associated with two heavy quarks decaying to leptons. The proposed method is divided into two stages: an initial stage where a ZQQ and ZZ control region is defined, and a second stage where an extrapolation of the measured ZQQ and ZZ to the Higgs signal region is performed. It is found that the ZQQ background in the Higgs signal region can be estimated with 70% and 30% uncertainty for an integrated luminosity of 0.2pb−1 and 1fb−1 respectively. These uncertainties are dominated by the limited statistics in the ZQQ control region. The systematic uncertainties come from the knowledge of the distributions of the various discriminating variables used in the lepton identification. These distributions can be obtained from early data by exploiting the lateral and longitudinal segmentation of the LAr calorimeter, and the inner detector (TRT and silicon). The main result of this work is that direct measurements may provide the only path to the Higgs discovery in the H to 4l channel during the first years of LHC running.