W Mass as a Calibration of the Jet Energy Scale at ATLAS

1. JET RECONSTRUCTION AT ATLAS The ATLAS calorimeter is non-compensating. Its calibration may be performed either globally or locally. Global calibration is a top-down technique where hadronic objects from specific physics processes are reconstructed relative to a fixed (global) electromagnetic scale. The weights are subsequently applied to calorimeter layers and individual cells based on the deposited jet energy density. The local calibration method is a bottom-up approach which starts with the response of cells and cell clusters, to which sets of weights based the ratio of the deposited electromagnetic to hadronic energy (EM fraction) and determined statistically are applied. From such calibrated clusters jets are reconstructed. In what follows we present a simulation study designed to assess the ATLAS calorimeter performance through the jet energy scale (JES) determination from the top pair and VBF H →WW → lνqq̄ simulations. The work on the universal JES definition is still in progress. For the study presented here we use two simple formulas: