Tau energy Calibration in the ATLAS Experiment

Here we describe the energy scale calibration of hadronic $\tau$ decays and the associated uncertainty in 4.5 fb$^{−1}$ of data at $\sqrt{s}$ = 8 TeV recorded in 2012 with the ATLAS detector at the LHC. The calibration is based on simulated $\tau$ decays, while the systematic uncertainty is estimated by propagating single particle response measurements to the individual $\tau$ decay products, namely charged and neutral pions. The systematic uncertainty on the hadronic $\tau$ energy scale for $p^\tau_T$ > 20 GeV and |$\eta^tau$ | < 2.5 is found to be ≤ 3% for the hadronic decay modes with exactly one reconstructed track, and ≤ 4% for the hadronic decay modes with at least two reconstructed tracks. The systematic uncertainty is obtained with a deconvolution method, and is checked using an in-situ analysis of the visible mass of reconstructed Z boson decays into one leptonically and one hadronically decaying $\tau$. These two methods yield results that are compatible within the calculated uncertainties.