Determination of the tau energy scale and the associated systematic uncertainty in proton-proton collisions at sqrt{s}= = 7 TeV with the ATLAS detector at the LHC in 2011

This note describes the hadronic tau decay energy calibration and a new data-driven method to determine the systematic uncertainties on the energy scale. The systematic uncertainty on the energy scale of hadronic tau decays is calculated using the convolution of the individual visible tau decay products, namely charged and neutral pions, following the method employed for jets in 2010. This procedure is employed to assign the systematic uncertainty for the tau energy scale in 2011. The final systematic uncertainty for multi-prong tau decays, is on average 3%,and up to 5% in in the 0.8<|eta|<1.6 region for PT <20 GeV. The final systematic uncertainty for one-prong tau leptons is less than 3% in the region |eta|< 0.8 and slightly larger than 3% in the region 1.3 < |eta| < 1.6. The systematic uncertainty quoted using the deconvolution method, in the region where no test beam data are available, is confirmed by using the reconstructed visible mass calculated from Z → tau+tau− decays.