Measurement of jets production in association with a Z boson and in the search for the SM Higgs boson via H $ \to \tau \tau \to \ell \ell + 4 \nu$ with ATLAS

Three measurements focussing on the understanding of jet final states in ATLAS, in di-jet, Z and Higgs boson candidate events, using data corresponding to an integrated luminosity of 35 pb−1 in 2010 and 4.7 fb−1 in 2011, are presented. In the first part, a calibration method, based on the transverse momentum balance in di-jet events, is described. The method is used to estimate the uncertainty of the jet energy scale in the forward region. The results show that the parton shower models are limited in reproducing the results in data, mostly for jets of low transverse momentum. In the second part, the differential cross section measurement of the Z -> ll + jets process is reported. Phase space regions not been previously studied at other experiments are investigated. The models used for the theory predictions provide a good description of the data, within the relative uncertainties. In the last part, two contribution to the Higgs searches in the H -> tau tau channel are shown: the modelling of the Z -> tau tau background, and the modelling of jet final states. The Z -> tau tau background is derived from data and validated in the H -> tau tau -> ll + 4nu channel. The modelling of jet final states in simulations is in good agreement with the data, when low-energy pile-up effects are subtracted.